View Full Version : Derbi GPR Track Bike

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08-17-2015, 03:58 AM
PhotoBucket has decided to extort their customers. I've switch to using Imgur for the new stuff. You can view the older posts in this thread in two ways.

First you can use the Chrome browser with PhotoBucket fix extension (https://chrome.google.com/webstore/detail/photobucket-hotlink-fix/kegnjbncdcliihbemealioapbifiaedg).

Second you can view it with most any browser over at GPR Camp on the foro (http://gprcamp.com/foro) there. I've split it up into a number of threads.

Derbi GPR Track Bike (http://gprcamp.com/foro/viewtopic.php?f=15&t=37&sid=c8d982b1c1ca27d3b3795bf732c79d1e)

MT Mike's Track Bike (http://gprcamp.com/foro/viewtopic.php?f=15&t=71&sid=c8d982b1c1ca27d3b3795bf732c79d1e)

Cobra CX65 Mini Moto (http://gprcamp.com/foro/viewtopic.php?f=15&t=78&sid=c8d982b1c1ca27d3b3795bf732c79d1e)

PPMPR: Project Poor Man's Pro Race (http://gprcamp.com/foro/viewtopic.php?f=15&t=49&sid=c8d982b1c1ca27d3b3795bf732c79d1e)

Please do check out these threads. There's lots of great information within!


For sometime now I've been collecting parts that would ultimately end up on a bike to take to the track--kart track that is, not a full on moto race track. Just something fun to ride in an environment where you can push the bike a little harder, and not have to worry about things like cars, curbs, and other similarly dangerous obstacles.

Somewhat recent events caused me to change my plans a bit and accelerate this build. My Red bike (http://www.apriliaforum.com/forums/showthread.php?275584-Derbi-The-Red-Power) has seen significant abuse due to bad drivers (it's been knocked over ten times since the build), and vandalism. So that bike is sadly coming apart in prep far a rebuild. In the mean time a lot of its dinged up parts are being repurposed to the track bike where scratches and such are just a fact of life. I've been given lemons as it were, and it's time to spend the afternoon in the sun! :D

The idea for this bike is to basically take parts I have laying around, and assemble a fun ridable bike for the track. It's something I plan to do in stages with regular revisions as parts become available. The frame is from another project that was being assemble for a friend that gave up due to life getting complicated. So he sold me a roller. Most of the bits from that bike I wont be using, but the frame and swing arm were decent. They were sent to the powder coater, and came back all shiny black. I did this at the same time as the Red bike to optimize the discount, knowing that eventually I'd use it for something.

The frame when it was at the powder coaters a couple of years ago. Originally this was one of the infamous GPR75's that made it into the States. Ozzie from Cycle Imports brought 200 of these over in a couple of containers. Somehow I've ended up with three of them. :lover:


The bike as it was once mis-envisioned


Ed had suggested that for now I should take parts from the Red bike, and get the Track bike running--so that we could go ride at the Stockton track event (http://www.mopedarmy.com/forums/read.php?1,3886658). The Track bike and the Red bike on the way to Ed's where the swap will begin.


A track bike needs proper tires. These are Sava F001 (http://www.treatland.tv/sava-F001-racing-slick-tire-p/sava-f001-17x95-fslash-70-tire.htm) (95/70-17 ), and R001 (http://www.treatland.tv/sava-R001-racing-slick-tire-p/sava-r001-17x115-fslash-70-tire.htm) (115/70-17) track tires picked up from Treats (https://www.treatland.tv) to go on some 17 inch Derbi Grimeca (http://www.grimeca.it/en/) rims (the stock rim size for the 2000 GPR is 16 inch). My friend RedSix did a late night tire swap to get ready for the track.


After some time at Ed's we headed to the track, where I would have to do a bunch more work.


Speedy brought out some cardboard on which to set up shop, and my Sacto moped buddy's provided some necessary shade.





Most everything went pretty well, and I had a bunch of help from my friends. I wasn't able to get the bike started, so it didn't get to go on the track. Current belief is that it's an ignition issue. I harvested an HPI mini rotor that I had installed on my moped. The stator didn't fit all that well, so I may have to get a proper mounting plate made up if I can't get this one customized to work.


Some cool things currently on the bike:
Metrakit ProRace pipe (for an RS50)
Brembo RCS16 master
Risse Racing Shock (http://www.risseracing.com/mxdampers.shtml)
Sava F001, R001 tires
Poor Man's ProRace (http://www.apriliaforum.com/forums/showthread.php?310473-Project-Poor-Man-s-Pro-Race) Airsal 50mm top end
Metrakit 24mm PWK carb
Domino roller throttle (http://www.treatland.tv/domino-gas-cross-throttle-assembly-with-grips-p/domino-throttle-2311.03-02.htm)
E clip sprocket mounting (for quick sprocket changing ability)
2005 GPR clutch lever assembly
Trail Tech kill switch
Handmade aluminum oil pump block off cover
Lots of custom black powder coating action

08-17-2015, 05:58 AM
sounds similar to the last time i went to the track. i brought spare everything except for an ignition coil.

my ignition coil cracked in half coming out of the van ....


it should be ready for the next event, right?

08-24-2015, 04:35 AM
We went to the Sonoma kart track (http://simracewaydrivingschool.com/programs-experiences/go-karting/) today, and I had a chance to work on the bike. I figured it was an ignition thing. The plug was wet, which meant fuel was at least getting to the bike. I pulled the plug and verified that it was sparking. Then I repeated the process with setting the ignition timing. But it turns out the HPI doc didn't provide the correct information. I then remember that my buddies at Motomatic had posted HPI information (http://motomaticmopeds.com/blog/?p=1356) with regards to setting the timing. I then applied their research, and the bike started right up. :D

But I was out of time, again. But next week we should be going to Stockton (http://www.stockton99.com/little99_schedule.html) again, and I should be able to do some tuning. :}


08-24-2015, 10:04 AM
That sucks that the HPI documentation is wrong or not helpful. Why is it that so many performance parts companies are so bad at this part? Take the PVL magneto on my other race bike. Support and documentation is terrible! But hey, at least I understand the thing now and how it works because I dickered with the thing forever to understand how it works and what making changes resulted in.

08-24-2015, 02:47 PM
The Motomatic info is not all that different from the HPI docs, but the HPI docs have you set it to the other side of the center, and that's enough to make it not work. My friend Taylor suggested setting the timing to the third big tick from the left. This is where I currently have it set. I also had a bit of trouble centering the stator plate because the Puch plate doesn't quite fit the EBE. I had to modify the the stator plate. The mounting bolts are such that I wasn't able to make it so that I can easily rotate the plate, which means I have to pull the rotor, and reset it to make adjustments. Pain in the ass, but it works. :P


08-28-2015, 04:09 AM

08-31-2015, 02:16 PM
If you are ever in the market for another set of Showa forks I just got a set that I wont be using. Looks awesome, cant wait to get my rs50 back to the states!

09-01-2015, 06:43 PM
Hey D,

Thanks for the offer. :D

I've actually got another set that I'm going to being using. These ones have pits, and are leaking. Well, they have leaked. There's not much left in them to leak now. :P

If you be in NorCal you should come out to the track and play. When are you expecting to be back? It's been quite a while since I've organized a street ride around here due to the bad drivers that have incapacitated my street bikes. Eventually though I'll get that sorted, and organized some street riding action. :D

For now though I'm focusing on getting on the track. :)

09-03-2015, 12:26 PM
I from Washington so eventually I would probably make it down to norcal! But in December I am coming back but going to North Carolina. What are the class that you can race a 50cc in? is it that BATS club racing?

Also what the black seat looking thing? was that the oil tank?

09-04-2015, 12:24 PM
Great to have a bunch of extra parts lying around!

09-08-2015, 05:42 AM
Hey D,

The thing that I'm currently employing as a seat is the fuel tank. The folks at Cagiva used an interesting method to get the weight were they wanted it, and also created a place to store one's helmet!

The racing that's currently going on out at Stockton seems to be gaining momentum. I went to the most recent race. I probably knew about half the racers from the rides I've organized, track days, and moped riding. It was super fun. There's another race this month, and hopefully I'll be able to attend, although I probably wont race. They host open practice from 9am until an hour before the races start. Hardly anyone runs a 50cc top end. There is a class for kids that does, but even the mopeds are running around 75-80cc, and there are a bunch of ugly sounding 4T bikes out there too. I suppose that's to be expected, but the mopeds were beating them. ;p

One of my buddies got so inspired by the email I sent out to my friends after the previous Stockton race that he started building a bike to take to the track that very day. I was out at his place a couple of times this week helping out. Here's a work in progress photo.


The Forks

I also started working on the forks. Had the wrong seals though, so the fork repair will have to wait until I can get the proper seals. For those interested the stock oil weight for these forks is 7.5, at 175cc. Once I get the proper seal dimensions I'll post that info too. Because these forks do not feature adjustable damping, the easiest way that you can change the reaction times is by changing the oil weight. A lighter weight will make the response times quicker, and a heavier weight will make them slower. Adding more oil will change the progressiveness because there will be less air to compress. For the track, since it is smoother than most roads a faster response time would likely be preferred. So I'm going to try 5 wt this time.

It would also be possible to switch out the springs, or adjust the sag by inserting a spacer with the spring. I wont be playing around with either of those at this time.

There is a trick to working on these forks. You can't actually do it with hand tools because the bolt that must be removed will just spin. So you have to employ a power tool to remove the top socket head bolt. There's also a trick to putting the screw back in. There is a hole near the end of the shaft. You slide the spring over the shaft, and then slip a small auger into the hole. Spin the spring to get the nylon piece over the shaft, and then spin the bolt in. It's a bit tricky, and the manual doesn't explain any of this stuff.





09-08-2015, 09:49 PM
The fork seal says these numbers for the ID OD Height:

34.74 x 47 x 9

I found some different numbers listed for these forks, but that's not what's in them, and they are different than the Showas that are also used by the Derbi. I've successfully used the All Balls seals for the Showa forks with part number 35-1011, seal size 35 x 48 x 11, but the Sebac forks for whatever reason employ a different size. And interestingly enough some websites list the wrong size for the Sebacs. Which is how I ended up with the wrong seals. Additionally, the parts manuals for these bikes don't list the seal size either.

A couple of UK sites list seals is this size, but so far I've not found a dust seal. There's an older Guzzi that has the same size, but the dust seal is the old style wrap around. The Gilara Runner seems to have the same dust seal which is a 35 x 47.5 x 13. More research to be doing.

09-09-2015, 02:22 AM
Today we found a pipe for my friend's machine. :D


09-09-2015, 03:01 PM
Found some images of the seals on ped parts. These are the actual parts from Piaggio.

Dust Seal (http://www.pedparts.co.uk/product/1710/piaggio-gilera-front-fork-dust-covers-seals)
http://www.pedparts.co.uk/c/products/RAW/Piaggio_Gilera_Front_Fork_Dust_Cover_34mm_x_47mm.j pg

Fork Seal (http://www.pedparts.co.uk/product/2059/genuine-front-fork-seals--gilera-dna)

09-09-2015, 09:12 PM
This thread is great inspiration to get back out there! It's been a long time since Stockton

09-10-2015, 12:41 PM
looking good! I love that you are putting part numbers out there for people!

09-11-2015, 03:12 AM
Yeah I do a lot of that sort of thing. Partially because I can't remember them, and then also because I'm sure others can benefit from my effort. :)

When I first started getting into the whole Derbi thing I could't find anywhere that listed part numbers. I found braggadocios that would claim they knew how to do things, but didn't share any info, or worse made fun of people that couldn't figure it out. Very annoying people. I didn't want to be like that--so when I found stuff I posted it. ;)

09-11-2015, 02:56 PM
A bit more news on the seals front. The KTM SX 65 from around 2003 has a very similar size seal setup. It's not the same, but it might work.

All Balls Part #55-128
Oil seal 35x47x10

All Balls Part #57-139
Dust seal 35x47.5x11.5

All Balls makes kit (http://www.allballsracing.com/fork/56-143.html) that includes the oil and dust seals for about $30. I've gone ahead and ordered that kit. I'll let you know how it goes. I'm mostly concerned with the oil seal being 1mm taller. It's possible that the lock ring that keeps the oil seal in place may not be employable with the slightly taller seal.
All Balls KTM SX 65 Kit Part number 56-143

Compared to the Sebac fork:
Oil seal 34.74 x 47 x 9
dust seal 35 x 47.5 x 4.8/13

Athena also makes a seal that is the proper size for these forks P40FORK455136 (http://www.athenaparts.com/eng/products/view/8522/mgr-rsd-34-7x47x9)

Adrenaline sells a Texnix oil seal (http://www.adrenalin-pedstop.co.uk/p-Fork_oil_seal_for_Rieju_MRX_50_RS2_etc__3474_x_47_ x_9-5081.aspx) that is the proper size.

Racing Planet sells the proper sized oil seal from Naraku NK158.20 (http://www.racingplanetusa.com/front-fork-seal-3474x47x9-gilera-runner-rieju-p-164622-1.html).

Interestingly a Tomos A35 main shaft seal (http://www.treatland.tv/tomos-A35-main-shaft-seal-35x47x7-p/tomos-main-shaft-seal-35x47x7.htm) is pretty close too: 35 x 47 x 7
The nice thing about the Tomos seal is that the height wouldn't be an issue.

If the All Balls oil seal doesn't work I'll source either the Athena or Texnix. That with the All Balls KTM SX65 dust seal should produce a viable affordable seal kit for the Sebac forks found on the 2002-2003 GPRs.

On this Moto-Guzzi site (http://www.motoguzzispares.com/pr/TheShop/index.php?f=e&Shnew=1&Model=17&ModelName=V7%20Sport,%20750S,%20S3,%20850T&Cat=ALL&CatName=All%20Categories&Sort=TitleAsc&spPage=20#) they list all of these bikes employing the 34.74 x 47 x 9 oil seal.

Fits Moto Guzzi Le Mans 1, Le Mans 2, T3, Le Mans 3, Mille GT (35mm Forks), 1000 SP, Convert, G5, T4, V65, Lario, V7 Sport, V35 Florida, Imola 2, Monza 2

09-12-2015, 08:19 PM
I was able to source some All Balls for the weekend. :D Stephanie over at KC Engineering found a set, and got them to SF this morning. I also picked up some 5wt fork oil. If it doesn't work out I can always put the 7.5wt in the forks. ;P The thing is since these forks are not adjustable the damping can only be effected with changing the fork oil. This will provide slightly less damping, where if I were to go to 10wt it would produce slightly more damping.



09-12-2015, 09:03 PM
I found the photos of the Showa forks I resealed for the Red GPR. Near as I can tell the design is the same. Could the parts be interchanged? It's possible. The sliding tubes (the lowers) are 35, so you could run 35mm seals. The potential issue would be if the Showa bottoms would work with the Sebac bushings. I don't have a measuring tool with enough resolution to check the dimensions. But what I might be able to do is see if the Sebac bushing would fit on a Showa sliding tube. It's entirely possible that Sebac just specs a slightly tighter seal for the same size sliding tube. I'll soon find out if a 35mm seal works on the Sebac forks. :eek:

Here are the numbers:

front fork seal set size all balls individual seal all balls seal set
GPR 1999-2002 35 x 48 x 11 35-1011 55-108

oil seals w/ dust ring dust ring kit
56-115 57-112








09-13-2015, 11:28 AM
Here's a fun little gadget that I picked up for the Monza only to find out that it didn't have a speedometer. That's fine I'll put it on the Track Bike. :P

Metrakit for a while made a unit sourced from Koso that features a tachometer, a temperature gauge, and a settable shift light. It comes with a couple of seeing units for the temp for use depending on the cylinder head, and a couple of wires for the tach, depending on the ignition system of the bike.

The red sending unit is the one employed with the Derbi, and for the ignition you can either go with the wire wrapped around the plug wire, or connect directly to the ignition. I'm probably going to go with the wrap wire as I've see people mess these up by connecting them incorrectly.

The unit is powered by a nine volt battery. This may seem weird but most track bikes don't generate power, and all accessories tend to run on a constant loss battery. Since for the Metrakit bikes most folks only run this dash a nine volt is all you need.




09-13-2015, 04:18 PM
That style Koso is what I was looking at. Good choice

09-13-2015, 10:48 PM
If you're running a programmable cdi, run to the dedicated tach out wire. I've had so many problems using inductive style rpm leads. I think maybe for just a tach it is alright, but since I also use it for gear calculation, datalogging, and other un-needed wastes of time, I needed much more accuracy than the inductive pickup could provide

09-14-2015, 02:13 AM
I'm pretty sure Koso makes these for MRD, however modded to go over 16k RPM. The inductance seemed to work today. I have to make a proper mounting plate for it. I just zipped tied it on the tripples for today, and it angled a bit which was hard to see while riding. Really though, the temp gauge is of more importance to me. :P I like the trail tech temp gauge, but the MRD temp display is really large, so you can actual see it at track speed. :D


Today was the first day I ever got to ride slicks at the track. It's really nice. :P The Derbi had some issues today, but none of them were the fault of the bike--my mechanic needs to do better. :eek:

I was having a lot of trouble getting the bike to run. With a bit of investigation I found that my intake manifold had deteriorated massively.


While I got the fork seals in time, I didn't have the opportunity to install them. So I grabbed the forks from the Red bike for today. :rolleyes:


But pretty quickly things went together this time. Got the forks installed, installed the MRD, but then had issues with the intake.


Near the end of the day things cooled down a lot, and the Derbi started running decently enough that I decided to take it out on the track. It was nice because most folks had already gone home, and there were only four or five of us on the track. This allowed me to do some sorting of the bike on the track. The bike is a lot faster than I am. These Derbis really like to be ridden. They want to go fast. Which is great, but it helps if you are a fast rider. I'm going to have to work on that one! :lol:

Ed came out on one of his bikes, and gave me a tour of the track showing me some lines. This greatly improved my getting around the track. Thanks Ed! :)


There are still a bunch of things I plan to do on this bike, but for now it running, and it was a total blast to be riding it out at the track. :lover:


Miku daiyou!


09-14-2015, 07:51 PM
Okay got seem sleep after a long day out to the track. :P Here are some photos of some of my friend's bikes. Lots of cool stuff is showing up out there. :D I didn't get any photos of Ed's bikes this time, but they are on the first page of this thread, and I'm sure there will be opportunity in the future to post them. ;)

Ben's Pocket Master 2T--I think these are 65cc, but I'm not sure.


One of Ben's friends has this sweet pocket master.


Garrett's Moriwaki 250 4T


Garrett's YSR/CR125 2T


Kyle's Shark Bike RS125/85 2T


Alan's Kayo 125 4T


Darin's NRS with a 125 4T Check out the carbon fibre front fender.



Emmy's SG 50 2T Yeah this is a wickedly cool fifty!


09-14-2015, 08:51 PM
nice set of bikes........

09-14-2015, 11:38 PM
ugh that looks so rad. those md250s are no joke

09-15-2015, 01:32 PM
Yeah it's super fun out there. Lots of cool bikes, cool people, and a fun track to ride around. :D

09-15-2015, 05:11 PM
Emi's bike looks sick! Can't wait to see it in person!

09-16-2015, 07:52 AM
I love the Moriwaki and the RS125/85. I didn't realize people were racing Moriwakis on kart tracks. The sprockets on those "Pocket Master" bikes are ridiculous!

Emmy's SG 50 2T Yeah this is a wickedly cool fifty!
That is super trick. It took me a while but I finally found some more info, albeit limited.


Any idea on who imports them? Cost? Is that bike mostly as delivered or has it been customized a lot?

09-16-2015, 08:15 AM
Cool I haven't surfed this forum in over a year I'd think! Got some catching up to do! lol

09-16-2015, 12:54 PM
Scott! It's great to see you posting again. ;D


It's amazing what some people bring to the kart tracks. Sure there are lots of Motards out there with huge 4T ugly sounding engines, but this weekend there was even a Ninja 250 out there (you can guess why I didn't take a photo of it!). But usually the tracks run different heats so that a pocket bikes doesn't have to compete with the big Motards and such. Although a couple weekends ago at the Sonoma track my friend Violet was out on her first lap, first corner, and a Motard ran straight into Violet crashing her out. That messed up the bike enough that it was the end of her day. On the track I kind of see Motards as SUVs. They ride like them, sound like them, are out of control like them. Just ugly.

Nice find on the SG link. When Paul picked up the SG for his daughter I went looking around to find info on it too. There's precious little to be found. Mostly what I found was their pocket bike info. From what I'm told that is a water cooled 50cc engine with a six speed gear box. I heard that it was $13K. For that kind of money I probably would have sourced a MetraKit. But it's a cool bike--everything on it is quality, and I can't keep up with Emmy--not even close. :P

I don't know who brought it in, but if you really want to know I can find out, and get back to you with the info.:D


There's another kid named Max that comes out to these tracks with a Metrakit. It's a newer one with the Metrakit engine. Max has been racing in Europe is some sort of Metrakit class. He's been racing kids two years older--and yet they are smaller then him, and Max isn't a huge kid. We just grow them larger here in the States! Max has been getting on the podium which is fantastic. If you watched the Red Bull Rookies then you know that the Americans generally don't do very well in Europe. We don't have the support systems here in the States to groom young GP racers. So to see Max going out there, and getting on the podium is amazing. He's fast though. On the Moriwaki even Garret has to work hard to keep up with Max on the Metra 50. :D

I'd really like to see the Cobra Dirt bike (http://cobramotorcycle.com/v3_default.asp) cats get into miniGP. They have an amazing two stroke engine that could be the platform for a great miniGP bike. Cobra makes a very competitive MotoCrosser built here in the States that's giving the Japanese, and even the European manufactures serious headaches. They do it by not following the Japanese 80/80 method. Which is give you 80 percent of what you want for 80 percent of the price. I mean that works, and it's a fantastic way to sell crappy Civics, but is that really what you want in a race bike? Anyway, the Cobra engine is sweet, and would be a little GP dream.



The RS conversions though are probably the best bike for us older folks. It's a real GP bred race bike, and an 80ish engine is all you need at the cart track--well unless you are hunting Motards. Speedy has a KX100 engine in his RS. It's probably the nicest of the RS bikes out there.


09-16-2015, 01:45 PM
The Honda rs chassis is a tight fit for anybody over 5'6, Jesus Christ, the aprilia rs50 is bigger

09-16-2015, 02:57 PM
It's true that GP racing tends to favor the jockey body types. :P

But the reason the GP RS is better than the road RS for the track is that it is much lower to the ground. Look at the photo of Speedy on his RS. To get a GPR, or an RS50 like that in the corner requires a lot more effort. I'm not saying that you can't have fun on these bikes, hell my "track bike" is a GPR, but the GP bike stature is just better at the track than the Replica bikes.


09-18-2015, 02:19 PM
Found some of the Moped action that's been happening, and a photo from Sonoma back in 2013 when I took the Monza to the track.

These are a couple of race mopeds. The white one is a Derbi Variant, and the black one is a Derbi Revolution. These bikes are screaming fast. Not your grandma's mopeds. They were actually able to out ride Garret when he was one the Kayo at the race last month.


Here we have me with the Monza, MT Mike with his RS80, Speedy with his RS85 (it's now got a KX100 in it), and Paz with his RS250F!


09-18-2015, 11:37 PM
It's true that GP racing tends to favor the jockey body types. :P

But the reason the GP RS is better than the road RS for the track is that it is much lower to the ground. Look at the photo of Speedy on his RS. To get a GPR, or an RS50 like that in the corner requires a lot more effort. I'm not saying that you can't have fun on these bikes, hell my "track bike" is a GPR, but the GP bike stature is just better at the track than the Replica bikes.


sure, the height has some to do with it, but it's the entire package. the gp bikes weigh like 160 pounds, it is ridiculous. my rs weighs 204 lbs and the road 125's weigh almost 280, don't they!? so they are smaller, they are lower, they are significantly lighter, they have more aggressive frame geometry, their frames are stiffer, the whole package is a step up. if you were to take a street RS and lower it would it improve that much? I lowered the front end just a little bit and raised the rear to get the bike to turn a little nicer, but i'm not sure how much of an improvement it was because the bike went from going around the outside of ninja 250s at the track to still going outside ninja 250s at the track.. so it's like, great, i don't have logical laptimes, i'm still in like the 1:40's or whatever, not really that great.

09-19-2015, 01:20 AM
Sure it's the whole package. One is a GP race bike, and the other is a replica street bike for Sixteeners. :P I don't know what the Aprilia street RS125 weighs, but my Cagiva was pretty heavy. The wheel upgrade helped a lot though. ;)

Did you ever read that Moriwaki vs the Aprilia RS125 shootout Motorcycle.com (http://www.motorcycle.com/shoot-outs/moriwaki-md250h-vs-aprilia-rs125-shootout-89190.html) wrote? The RS didn't have a chance, and it lost in every way, except retail price. It's a street bike that some asshole decided to pretend was a track bike. And well it suxors on the track, as one would totally expect. Way too heavy, not enough power for the weight, and the CG is way too high. The RS50/GPRs suffer from very similar issues. So really they don't make "good" track bikes. But you can have fun on them at the track, and the cost of entry is very low.

Out at stockton if I were to race my GPR I would be in the same class as the Moriwaki. 33 real horse power against the little Derbi--the Derbi wouldn't have a chance.

With regards to lowering the street bikes, It wouldn't work because you'd screw up the geometry. If the swing arm doesn't have at least a slight incline from rear to front the suspension suffers greatly. Now if you chopped up the frame to put the rider lower that would be an improvement, but almost no one goes about lowering a bike that way, they nearly always do it by fuxoring the suspension.

But the lower bike has a huge advantage. When I took my moped, which is big for a moped, but about the same rider height as the RS race bike, it was much easier to navigate the kart track than on my GPRs. The GPRs have a much higher CG, and without speed to deal with it like what the MotoGP bikes have, it's hard to get the higher CG to navigate the lean angles that you can get with the smaller bike, at the lower speeds.

Note that this Motorcycle.com test is bullshit because it's not really comparing the 4T with the 2T, it's comparing a GP bike with a Street bike--on a track! They admit it in the video at the end, but still I hate this sort of sensationalism. If an honest to goodness 2T vs 4t comparison were to be done the 2T would shine on the track. Physics is physics.


09-20-2015, 01:13 PM
Found some more photos from 2013. Here's MT Mikes' RS, Speedy's RS, and Violet's NSR.




09-21-2015, 01:23 PM
Those cobra motors seem really legit for under 100cc! Do you have any pics of you on the derbi?

09-21-2015, 07:50 PM
The Honda RS125 track bikes is pretty serious along with the others in it's class. I used to have one as well as had time on the TZ125 also. The powerband on those GP bikes is pretty fierce. My RS was a 96 with 97 pipe and other bits.

When I sold it I kept a set of wheels with the rains on them. Idea is to fit them to my Moriwaki 80 at some point.

09-22-2015, 02:55 AM
Dcrac3r, it looks like a great engine. And they are made in the States too. If Cobra started building miniGP action it would carry a lot of weight, because of the success they've had in the dirt. We really need that sort of thing in the States.

Scotty that 80 you have is pretty slick, but yeah the RS is a real race bike.

09-22-2015, 03:00 AM
I've been working on another project which I'll probably start posting about tonight. While going at it I found some bits for the track bike. I sadly admit my bike isn't up to spec yet. I have some things to do like catch bottles. Thankfully I found them tonight. :D I also found some nice Malossi reeds, and a silencer that's better fitted for the track--it's going to need some cleanup, and probably a repacking too. The carbon Jolly Moto is just too nice for the track.




09-22-2015, 04:10 AM
HRC catch can?

09-22-2015, 04:29 AM
I bought a bunch of parts from Todd--he had bought out all of the Rocket Ranch bikes. Lots of strange stuff showed up. I've been enjoying the bits from that haul for years, as have my friends. :P Although the bottle could have come from somewhere else too.

Yes all of that, and more fit into the Saab. :eek:


09-22-2015, 05:43 AM

09-22-2015, 01:12 PM
I bought a bunch of parts from Todd--he had bought out all of the Rocket Ranch bikes. Lots of strange stuff showed up. I've been enjoying the bits from that haul for years, as have my friends. :P Although the bottle could have come from somewhere else too.

Yes all of that, and more fit into the Saab. :eek:

With all those spares can you spare a front brake for my track attack Derbi? Mine went on your Moped a few years ago

09-24-2015, 04:57 AM
I was out on the BMX bike today, and stopped into visit my moped buddies. Paz had this for me. Some seat padding for the tank area. :D


09-29-2015, 04:17 AM
I've been putting so much effort into the street bike that the Track Bike hasn't been getting much attention. Since I posted about the things I got from Todd it seemed like a nice time to highlight the effort of my buddy Levi who is nearly finished with his Senda project. I hooked him up with a bunch of things including the frame, forks, seat, tank, and a bunch of other bits, but really the magic of this build was all Levi. He's a master with this stuff. He's got a build thread (http://advrider.com/index.php?threads/derbi-enduro-trials-bike.1022269/) up on AVrider that's totally worth checking out. :worship:


10-02-2015, 04:21 PM
I didn't make it out to the track last weekend, but Ed and his son did. They both took second in their classes! Here's Ed on his GPR, and Alex on his pocket bike.



10-11-2015, 02:05 PM
Found this today. :)

These results are from when the engine was installed on another bike with a different pipe, and stock ignition. I'm sure things are likely to be a bit different now. :lol:


10-20-2015, 07:06 AM
Today was a really long, and really cool day. :)

We started by crossing the bridge and heading down to LA.




MT Mike has been looking for a second bike for the kart tracks. His RS with the CR80 is being modded with yet a third engine, but it's taking some time. Plus, a number of us are getting set up with Derbi GPR track bikes. When folks have closely matched bikes it's just a bunch more fun when riding together.

A couple of brothers, Ed and Alex, in LA use to race a Derbi in SoCal in the early and late 2000's. We got to hear a bunch of fun stories from them. They have since moved on, and put their bike up on Craig's. I saw their post, and shared it with Mike--who decided to go for it. The drive down was quite nice. It rained a bit in LA, and then the drive back tonight was uneventful--which is a very good thing! :)

These photos are pretty lame, as they were basically taken in the dark. But they should give you some idea of how cool this little bike was in it's day, and how we should be able to bring it back to a significant percentage of that glory.


















10-20-2015, 08:40 AM
I didn't know those were steel frame

10-20-2015, 07:03 PM










10-20-2015, 08:08 PM
The mychron3 still works. That's a plus!

10-20-2015, 08:38 PM
Yeah this whole bike is just a treat. Sure it's seen some better days, but everything about it tells a story. You can tell Alex and Ed had a blast with this bike. :)

So for a bit of effort hopefully we can bring this bike back to some fun riding action. :D


Oh hey Matt, didn't catch your post. Yeah until the Benelli frame the GPRs were all steel. And yet it was still lighter than the classic RS. :lol: (actually I don't know if that's true or not!)

FDG--dood! I saw your CB350 build. That bike is so sweet--you can haz skillz. :worship:

10-21-2015, 03:17 PM
And so the process begins. I stared out with something easy--the silencer came in pieces, and needed a repack. Pretty easy to do. You can get the packing material from lots of places. I usually go with the $9 FMF stuff (http://www.treatland.tv/fmf-2-stroke-muffler-packing-EVERLAST-p/fmf-baffle-packing-78-1011.htm) from Treats. Since it was already apart I didn't have to drill out the rivets. Nice thing too as the Arrow has a bunch of them. :lol:

So I started out with some cleaning. Then rolled the packing onto the inner perforated cylinder, finessed it into the carbon fibre tube, installed the end piece, and riveted it back together. The unit has seen come crashes so I need to make some adjustments to get it back together. It came out nice though. :)

I need to do this for the Metrakit silencer for my bike, but I only had enough packing material for one silencer, and since I can run the Jolly Moto can on mine for now Mike's bike won out. ;)











10-21-2015, 03:35 PM
FDG--dood! I saw your CB350 build. That bike is so sweet--you can haz skillz. :worship:

Thanks man. It's still a work in progress and nowhere near as developed as I would like but it's a platform to get started and keep modifying. Jim Wulzen showed me a trick way to modify the front brake plate to create an air inlet scoop that I'd like to try with a spare brake plate. And I'm not yet convinced on the XL250 front end geometry (fork offset). I'm considering some CNC triple trees. And I'm not yet happy with the steering damper setup. 68mm stroke ohlins is too short (steering limited) and 90mm is too long (fouls against the inside of the bodywork). If I could mount it up top a la Ducati 916 I would but that would require some gas tank surgery. But that is probably my best bet at this point as it keeps it furthest away from harm.

As soon as the CB350 is done I'm building a free tech 50cc racer to tear up the local kart track.

10-21-2015, 03:47 PM
One of the things missing on MTTB (MT's Track Bike) was the Woodruff key. The docs state that it's a D6888, but that seems to be a standard (http://www.fullermetric.com/products/pin/din6888woodruff_key.aspx) rather than a size. So I'm going to have to source one for it. But they seem to be relatively reasonably priced (http://www.umicompany.com/catalog/06888a5-0365). Of course you don't really need the key because you can set it with your ocular unit.


10-21-2015, 03:51 PM
As soon as the CB350 is done I'm building a free tech 50cc racer to tear up the local kart track.

From what I've seen of the 350, that will be something with which to be concerned! I'm looking forward to it. :)

I have a similar Ohlins damper that came with my RSV (I put the stock one back on it when I sold the bike as stock). I want to install it on my Black GPR. And yeah, coming up with a good solution for installation is a challenge.

10-21-2015, 05:17 PM
I'll need to source the proper gasket, but here it is on the bike. ;) Yeah a rivet didn't hold, but I'll fix it. ;)


Next up is the carb. It's a Mikuni TM24 by the looks of it.




With the carb off I stuck the camera into the intake to see what's in there for reeds. Looks like the stock Derbi reed cage with some carbon fiber reeds. This are probably very nice.


10-23-2015, 05:04 PM
Back on the MTTB action today. Took apart the Mikuni TM24, and did some cleaning up. It had some yellow slim going on in there.


Lots of parts


Going back together


Ready for the bike


10-24-2015, 09:17 AM
Tora tora ive just been looking at the brothers bike and interested in the ignition on it is that the ducati ignition ? And does that cdi have a built in coil it looks to be wired straight to the plug ?

Sorry for my lack of knowledge but im at the point now where i need to ditch the rev limiter so i can go for the xtreme kit :p

So my plan now is to get an rs50 stator and wire it up to the ducati ignition, is that all id need ?

10-24-2015, 12:54 PM
Hey Matt,

The stock ignition on the GPR is made by Ducati. It is a CDI, and the CDI unit and coil are one integrated piece. Now a couple of companies make an aftermarket CDI unit for the Ducati ignition. These have a better curve with a higher peak value. You could upgrade that unit. I think Treats sells them. But before I get to that, and I will cover it in detail, I would like to address the fact that these mods don't take into account the weight of the flywheel. When going for a performance ignition this is a crucial aspect. So I personally wouldn't bother with any of these solutions. Instead I'd look for a better suited ignition such as the HPI mini rotor (http://www.treatland.tv/SearchResults.asp?Search=hpi+). It's easy to put this on the Derbi engine because it shares the same taper as the Puch (http://www.treatland.tv/PUCH-HPI-CDI-mini-rotor-ignition-system-p/red-puch-hpi-cdi-90.htm). I don't know the taper on the AM6 crank, but I'm sure it could be looked up, and then correlated to the proper HPI unit. For a track bike I would suggest the HPI inner rotor (http://www.treatland.tv/PUCH-HPI-CDI-ignition-system-p/puch-hpi-cdi-ignition-coil.htm).

http://www.treatland.tv/v/vspfiles/photos/RED-puch-HPI-CDI-90-2T.jpg http://www.treatland.tv/v/vspfiles/photos/puch-HPI-CDI-ignition-coil-2T.jpg

Okay so here's the Top Red Box CDI unit on Treats (http://www.treatland.tv/TOP-performance-digital-variable-cdi-box-p/top-performance-box-9921690.htm)


And here is some info on this ignition that is posted up on Two Stroke SE (http://www.twostroke.se/product.asp?product=22960).

Top Performance - CDI / ignition coil (Digital)
Price SEK 1299.00

In Stock
Art.nr: TOP-9921690
Unthrottled Digital CDI with variable ignition point

CDI box with ignition coil from Top Performance with variable ignition point.

An absolutely brilliant product for those who want to trim their moped and do not want to replace the entire ignition system and keep on setting the ignition manually.

This CDI box has been designed for Minar Ellis AM6 engine with the 6-spoliga Ducati ignition plate but also works to Derbis ignitions which also has the 6-spoliga Ducati ignition plate.

When the original CDI are equipped with the ignition point throughout the registry to have the Top Performance have developed this product which has an internal microprocessor that allows the spark advance automatically adjusted the more speed engine and thus optimize the ignition point.

The CDI also has a very good ignition control called "Power Control", which ensures that pre-ignition is prevented, which leads to a cleaner ignition.

This ignition control also ensures that you get a longer life for both ignition systems and spark plugs.

Other great advantages are that fuel consumption is reduced by this also air pollution.

This kit contains the following:
1 st - CDI
1 st - Coil with 5 kOhm spark plug cap + cable
4x - Kardborrebitar for mounting

NOTE! This product is intended to be combined with Top Performance 70-75cc cylinderkit in their Redline series but also functions to be combined with the equivalent cylinder kit.

IMPORTANT NOTE!: this CDI kit is not combined kits in the 85cc class or cylinderkit with extended stroke bout as this may cause damage to the ignition and cylinder inserts.


Metrakit makes a CDI unit for the Ducati ignition too, part number: MK846R0311 (http://www.twostroke.se/product.asp?product=10497)


Metrakit - CDI (unrestricted)
Price SEK 549.00

In Stock
Art.nr: MK 846R0311
High quality CDI from Metrakit
A high performance CDI from Metrakit.
Delivered completely unrestricted, which gives you the right effect!
This CDI ensures that you get a higher speed stop and a better accelleration.
To mount the CDI is very simple, to simply remove the original CDI box and replace it. To then connect the cables is very simple as the colors are the same as those used on the original CDI'n.
On this CDI'n is 4 pins:
-1 Red
White -1
-2 Green
NOTE! This CDI is only compatible with Ducati ignition system with six coils.
Not suitable scooter models 2007 -> with the new ignition system from Dellorto

And Top has another unit, the Yellow one (http://www.twostroke.se/product.asp?product=8622).


Top Performances - CDI box (Ducati) unthrottled
Price SEK 499.00

In Stock
Art.nr: TOP-9910150
Unthrottled CDI box with '' Power Control ''

Top Performances - unrestricted CDI box to Ducati ignition.

An unrestricted CDI box without revolutions stop and the "Power Control" from Top Performances.
The box is of high quality and is designed and developed to optimize ignition on your moped.

The CDI also has a very good ignition control called "Power Control", it ensures that the pre-ignition is prevented, which leads to a cleaner ignition.

This ignition control also ensures that you get a longer life for both ignition systems and spark plugs. Other great advantages are that fuel consumption is reduced by this also air pollution.

Motoparts CDI-box fit 6-speed Minarelli AM6 engine and other mopeds / motor models that use Ducati ignition with six coils.

To mount the CDI is very simple, to simply remove the original CDI box and replace it. To then connect the cables is very simple as the colors are the same as those used on the original CDI'n.

OBS !! This is a product developed for competition use only and may not be used if the vehicle will be used on public roads NOTE !!

Not suitable for: Yamaha / CPI-models from 2007 ->

NOTE! It is important that the earth wire on the CDI box proper contact when mounting otherwise there is a risk of CDI box damaged.

(Note: the text below only applies motocross scooters from the CPI)

To use this box on the CPI:
On CPI-models the cables different original equipment, but this CDI can be used if you connect as follows:

- There are five wires to the original CDI's:
Black, Black / White, Black / Red, Orange and Red / White (All of these, you should cut off so you can connect them to Stylepro CDI's).

- Black / white cable to the outer green pin on Stylepro CDI: n (stop button function).
- Black / Red connected to the other (penultimate) of the green pins on Stylepro CDI: n (ie, the next stop button).
- Orange connected to the white pin on Stylepro CDI: n.
- Red / White cable is connected to the red pin on Stylepro CDI: n.

- The black wire is the ground wire to the original CDI set, it does not need to be grounded when Stylepro CDI are equipped with their own ground wire (black with cable lug).
The black cable on Stylepro CDI: n connects you to the earth.

- The black and orange cable to the original ignition coil need not connect to anything. They can cut and Stripa to the frame or similar.

11-05-2015, 08:33 PM
Well it's been a minute! If this was my bike I wouldn't have worried so much about the woodruff key, because really you don't need them. But since it's not my bike I wanted to be proper about it. ;) I ordered one from Treats, but it must have gotten lost on the way home because it wasn't in the bag when I got home. So I went the next day to pick it up. And I had ordered the wrong one! So I pulled one off of another bike, and then went to Treats. Will hooked me up with the correct one. I should have asked him the dimensions. He did say it was like a Puch stator side, but skinnier. ;)



I did a bit of cleaning before the final assembly--since it was a good opportunity. To set the torque I pulled the plug, and employed a piston stop. Some folks freak out about this method, but really the torque on this nut is only 35-45Nm so it's not a big deal. The plug looked good. :)



Then I drained the old gas. I had no idea how long it had been sitting around, so I figured it should be drained.


I also installed the carb. Then adde some fresh pre-mix. :) Then I turn on the MyCron, put the tranny in second, turned on the fuel, and turned on the choke. Gave the throttle o few twists, pushed, and let out the clutch. Magic! The bike started right up--even the MyCron tach was working. :) Of course then I had to shoot a quick video, and send that off to Mike. I found out, sadly, that feature only works with iPhones. :( He's got one of those super fancy Android units. Oh well. I'll have to remember the PW to my youtube account, and upload it there. :D

After all the excitement it was time to give it a bit of a washing.





It's cleaning up nicely. :)




Then it got dark and cold. :( I shouldn't complain though, because at least it's warm enough to wrench outside of a good part of the day. ;)

11-18-2015, 08:30 PM
We are considering a day to the track while most folks are out shopping, but damn it's going to be a cold day in Stockton!


11-19-2015, 11:02 PM
Had a chance to pull some plastics off of Mike's bike for a bit of work. There are some cracks, and Mike want's the bike to be white.




11-20-2015, 07:06 PM
Look like it's going to be pretty easy to sand off the blue.


Replaced the bent bar.


The exhaust manifold. This is from the Arrow pipe.




Went to bleed the brakes only to find that the master is leaking like on the Silver Bike. :(


11-24-2015, 08:31 PM
This is something I've been wanting for quite a while. They aren't really expensive, but you do have to actually order one for it to show up. Previously I would employ 50ml centrifuge tubes to measure out oil for forks. This 250ml graduated cylinder (http://www.amazon.com/Plastic-Liquid-Measurement-Graduated-Cylinder/dp/B0094EEGMG/ref=sr_1_8?s=industrial&ie=UTF8&qid=1448415006&sr=1-8&keywords=cylinder+250ml) should make the job much easier. ;)


11-26-2015, 11:26 PM

Tomorrow we plan to head out to the track for Black Friday. Ben and I did some bike wrenching today. I used the Saab for transport. I know it's silly, but I feel a bit giddy when I'm around this bike. :)









I didn't get good photos, but I added this choke lever that I got from Treats (http://www.treatland.tv/domino-choke-lever-2172-86-p/domino-choke-lever-2172.86.htm). It's going to work out well. It did require some pretty serious modifications to get it to work though! :lol:


Some photos of Ben's pocket bikes.





11-27-2015, 12:38 AM
question: when you lowside, whats going to prevent the tank from rubbing through?

second question: is that comfortable to sit on with no seat? lol it looks really uncomfortable

11-28-2015, 03:07 PM
Black Friday was a nice day to ride at the track, but getting to the track took some effort due to all of the crazy shoppers clogging the freewayz! Also the temps were quite cold. About 13°C at the warmest. We were probably riding most of the day in even colder temps. But it didn't feel bad at all. Sure it wasn't the track sticky 25-30°C we were enjoying over the summer, but it was fine.

This time I went out with my Pocket Bike friends--Ben, Al, and Jordan. There are six bikes in the back of this truck. :D




Ben, Al, and Jordan all use to race pocket bikes, and they are fast--like a squadron of Tie fighters with amped up Polini engines. I can't even pretend to keep up with them on the track. Oh sure my bike is capable, but I'm not. :lol: I have a lot of work to do to get back to my old riding form before the Honda Driver took me out. The GPR ran pretty good. I replaced the intake with one that isn't perforated. :lol: But it's not the right size for the carb, so I'm going to have to source a proper one for the bike. The Domino choke lever was a much appreciated upgrade, and considering how cold things were, much needed too. This bike doesn't like to start with out the choke, and especially so when cold.

Because it was so cold I took it mellow on the track, and never once felt the tires slipping. Hey I just started riding again, I don't want to crash out. :eek: After the sun set we had some nice hot laps though. Ben was showing me some race lines, and I kept saying to myself--these are so much better! :)

We nearly had the track to ourselves too. Early on there were some carts, and yeah there were a few evil four strokers making things sound horrible, stinking up the place (yes four strokers stink way more than two strokers), and causing a ruckus. But most of those cats left early, and we were able to enjoy a mostly open track. We also got to run the track in both directions--Euro Mode, and NASCAR. :lol:






11-28-2015, 03:15 PM
Hey Matt,

It's plenty comfortable. Maybe a bit slippery, but once you get your weight on your legs it doesn't seem to matter at all. This bike is totally a work in progress. It was pieced together from parts I had laying around in an effort to have something to ride at the track. Over time you'll see it come together in a proper way. ;)

12-05-2015, 09:30 PM
Today was the annual Nor*Cal Dyno day (http://www.bayarearidersforum.com/forums/showthread.php?t=486683). Once a year they invite moto folks to bring their bikes in to see what they've got. It's generally a whole bunch of fun. They are super cool chaps, and a real boon to the community. This year they even had pizza for us!

Before heading over to meet up at Ed's I unboxed Mike's new RCS14 that he picked up from KurveyGirl. It's really sweet. That titanium banjo bolt weighs so little that you can't even tell it is in your hand. Kurvey throws that, some tubing, and a bunch of crush washer in with the RCS. Is's that cool, or what? I put it on the bike, but didn't have a chance to take photos yet. The reservoir for it has yet to show up--so I used one from a GPR rear brake for now. ;)


I brought Mike's bike in with the Saab. Ed took his van with his GPR, his son's KTM, and my GPR in the van.


Alex's KTM went first. I think it did around 7HP. Pretty respectable for such a tiny little bike. Alex is so fast on this bike that he beats both Ed, and I around the track--and Ed is pretty quick too.


Next up was Ed's GPR. His bike is really strong. It has all the cool Metrakit Pro Race goodies. He got well over 17HP!



Then we ran my bike. Almost exactly the same as the engine did three years ago. I was expecting better performance because of the better pipe, ignition, and carb. This is really challenging some of my preconceptions!




Sadly we were unable to get Mike's bike running well enough for even a single run. I think it's the Mikuni carb. I mentioned to Ed that I thought it might be the Mikuni, and his response was "I hate those things. I just gave mine away." Then he spent about 20 minutes trying to get it running too. Looks like we might have to get a PWK for this bike too. ;)

12-06-2015, 12:24 AM
couple of things

1) i think you need a better pipe match
2) ive never had the problems you guys have with mikunis

12-06-2015, 12:55 AM
The previous pipe that I ran was the Ninja pipe that I got from Treats. This was when this engine was in my Black bike. The current pipe is a Metrakit Pro Race. One of the best pipes you can get for these bike, and the same as I think is on Ed's bike. The dyno pulls the first time were done in 6th gear (I'm guessing), and this time they were done in 4th gear, but that shouldn't really make much difference. There is of course more time on this piston/ring combination, so it's possible that the pipe/carb/ignition is compensating for a tired piston/ring, but the engine does feel quite strong.

Also, it is quite possible, maybe even probable that I messed up the top end with my mods. :lol: The way to test it would be to get a stock version of this top end, put it on with all the same parts, and dyno that setup. But that's not likely to happen, because if this top end gets replaced it will probably be with the Airsal Xtreme. ;)

I think the Mikuni thing is just that they are worn out, and any carb that's worn out isn't going to perform at its best.

Or it could be that Florida air is different than California air. :lol:

12-06-2015, 12:58 AM
ah. i thought you had the modified jolly moto or welded modified whatever on it. must have been a different bike.

florida is at sea level with about 95% humidity ...

12-06-2015, 01:00 AM
Ed sent me photos of his dyno print outs.



Metrakit PR GPR


12-06-2015, 01:05 AM
I do have a Jolly Moto on the Monza, and I recently picked one up (years ago already!) that will go on the Black bike once I get it sorted--but it's one of those projects that takes years and years.

Here it is in mock up mode.


12-07-2015, 01:43 AM
Here are the scans of the charts from my bike this year.



12-07-2015, 02:11 PM
Here's the dyno of the 45 stroke Airsal Xtreme with the same pipe and carb that are currently on my track bike. I also found that the dyno run from three-ish years ago was also done with the 24mm PWK carb, so that's no longer a factor. :lol: Now the interesting thing is this dyno run was with the same carb and pipe as the dyno run on the engine currently in the track bike. They even both have HPI ignitions, so those are effectively the same. The air box is different, and maybe I need to do something about the air box on the track bike, but that engine was using the air box used on this dyno run back when it was in the Black bike (I know this is all rather confusing!). But what's interesting is basically with the only difference being the top end/crank configuration the peak power is in very different locations. So is the pipe really controlling the peak? I use to think so, but the data is messing with my head. :eek:


12-07-2015, 07:14 PM
Sticky Sava track tires for Mike's bike were the project for today. We employed Greg's bead breaker again--I was too busy getting a work out to take photos of that action, but here are a handful of nice ones, and one of the Brembo RCS14 Master. ;)

We also did a carb swap to see if the bike would run better. It ran a little bit better, but still suffered major bogging with the throttle open.

To start things off we used Mike's tire warmers. We got the new tires nice, and warm, but as it turned out we needed to heat up the old tires to get them off. They were really stuck on the rim--probably from having been warmed up previously. It was so much easier having help to mount the tires on the wheels. Didn't take hardly any time at all, and I'm not nearly as sore as I've been from previous tire outings.


Front tire on the bike. I should have taken a photo of the rear one too. Have to get that later I suppose. :P



And the pretty Brembo action. This is becoming a very nice bike. ;)


12-09-2015, 11:09 PM
I finally had opportunity to put the All Balls KTM SX65 seals into the Derbi forks today. Ed granted me access to his bench so that we could use the pneumatic action to loosen up the bolt on the hydraulic tube. I've not yet figured out a way to loosen this bolt with hand tools.

Now these SX65 seals aren't an exact match to the stock seals. So far the forks looks to be well sealed, but I wont know for sure until I mount these on the track bike, and do some testing. I really hope these work, because then we have a very nice solution for these bikes. I also intend to play around with the fork oil weights, and quantities. Those of you with a sharp eye will notice that I'm using 5 wt, rather than 7.5 wt. Yup, trying out a little experiment. ;)


The Forks: These are the 2003-2004 GPR Sebac forks. The require slightly different seals than the older ones. The 2002 forks do share the same seals, but those are anodized gold rather than silver.


I think I already showed how to disassemble these forks earlier in this thread so this is just the assembly section. Lube up the seal, and place it into the fork tube. It wont go in all the way, but it will slide down to the seat. With the new seal in the fork tube used the top cap to seat the seal. It doesn't take much force, but you want to apply it evenly. You will know it's in place because you'll be able to see the ring for the retaining clip.




Once the inner seal is in place insert the retaining clip.



Then insert the dust seal. You should be able to put this one in place with just your hands. It doesn't take much force, just a little bit of finesse.


Then slide the stationary tube onto the sliding tube. Insert the spring. Reach in and pull out the hydraulic tube. Add the nylon spring cap. Now it's time for the secret tip on how to do this. It's nearly impossible to hold the hydraulic tube to insert the bolt. So take a small screw driver, and insert it into the small hole in the top of the hydraulic tube. Rotate the spring so that the tube reaches high enough that you can thread in the bolt. Then torque the bolt.



These forks take 120ml of 10 wt fork oil. You can change the wt, and amount to change the dynamics of the fork damping. Lower weights will decrease the damping. More fluid will stiffen the forks. Grab your graduated cylinder (you can get these off eBay for less than $3), mark with a Sharpe where you want to measure to, and pour in the desired amount. Pour this into the fork. Insert and torque the top cap.


12-10-2015, 02:35 PM
We needed a nice affordable solution to the brake master reservoir for the Brembo on Mike's bike. I found some Chinese brand that was State side, and ordered up a few. They look pretty decent for what they are--now I just have to fashion up a bracket.




12-12-2015, 01:10 PM
Ed and Alex went to Stockton. Alex took second on his KTM. Ed ended up racing a bunch of motards. I think he took second--he's number 14 in the photo (the white GPR). I'll have to find out who took first. :P


01-06-2016, 02:23 AM
It turns out that the Sabac forks found on the 2002-2004 GPRs use 120mm of 10 weight! The inner top bolts should be torqued to 17Nm. ;)


I'll go back and update the previous post...

01-10-2016, 02:40 AM
Ed just picked this up for his son. It's pretty cool--but it is a 4T. :(

180cc, and it puts out about as much power as that 72cc Derbi GPR behind it! :lol:


01-17-2016, 04:24 PM
I've been posting PWK info in some of the tech threads, but I thought it would be nice to have them around in the Track Bike thread since I run PWKs on most of my GPRs. ;)

Here's a link to Duncan Racing's PWK tuning guide (http://www.duncanracing.com/TechCenter/KeihinCarbJetting.pdf).

Here's an exploded diagram and parts list for the PWK, and a needle chart.



Here is a nice graph illustrating the effect of the various circuits, and their interaction on the PWK.


01-24-2016, 10:17 PM
I went over to Ed's today to check out the GP0 that he just picked up for his son. Admittedly the 4T is a big turn off, but outside of that it's a really cool bike. Check out these photos. Note, that Ed replaced the stock 4T engine because it was too much for the class that he wants to enter his son. So he bought a Lifan 125 engine--which mostly just slipped right in.








01-26-2016, 03:02 PM
that shock looks familiar

01-26-2016, 04:38 PM
They snuck out to the track yesterday. If they had told me I would have gone too. :P I haven't heard the results yet. The bike was set up for a fat guy, but it's suppose to be for Ed's son, so they have to go through the suspension for a 60 pounder. :P

I didn't recognize that shock though, but it looks pretty nice. Really all the stuff on the bike looks really nice (expect for the 4T action).

01-27-2016, 04:52 AM
Alex on the GP0

https://scontent-sjc2-1.xx.fbcdn.net/hphotos-xpa1/v/t1.0-9/940948_936865619740958_7235258201533693808_n.jpg?o h=f78c35fa19f1d6d06c0e05328980bd2c&oe=573EFB24

01-28-2016, 12:42 AM
Speaking of Derbi Track bikes, check out this photo. Very few motorcycle manufacturers have racked up over 100 MotoGP wins. In Japan there is Yamaha, Suzuki, and Honda. In Europe there's MV Agusta, Aprilia, and Derbi. Here is Markie Marc getting number 100 for Derbi. :)


01-28-2016, 09:23 AM
That Ohvale GP0 is a trick bit of kit even if it is a 4-stroke. Looks like a racy Monkey Bike!


01-29-2016, 02:17 AM
In accord with yesterday here are a couple more Derbi MotoGP Riders.

Yuichi Ui


Mike di Meglio


02-03-2016, 11:36 PM
Lots of Action on Mike's bike today. I've been wanting to do this work for quite a while, but things like cold and rain keep causing delays. When we took his bike to the Dyno we were unable to get it to rev up. We finally had to give in and not test the bike. Which was a real shame because knowing its power curve would be quite interesting, and nice to compare to our other bikes. Just have to wait for the Next Nor*Cal Dyno day.

Today I just plodded through things. First I did an inspection of the reeds. They looked great, and they hold succession too.


I then did a visual inspection of the cylinder, and piston from the exhaust port--this is pretty easy you just pull the exhaust off and look in the port. It didn't look brand new but it looked okay. Nothing to indicate why the engine wouldn't rev. Hard to get photos of this part!





Next was the leak down test. Again it worked great.



Next up compression. Here it produced around 6 bar (more than in the photo)--which is actually a bit on the low side, and I'm going to probably have to do more investigation on this one.


Then on to spark, because well maybe it was the ignition, but again I found it had good spark. The plug looked a little bit rich, but nothing horrible, and it produces a strong spark.



I did notice that the fuel filter wasn't filling up as fast as it should. So I think it might be the petcock. I'll have to go to Treats and source a good one.



I did check the carb previously. I cleaned out the carb on the bike, a Mikuni TM24, and it was unhappy even still. So I grabbed the TM24 from the Monza (which I already had off the bike), and tested it on Mike's bike. This carb works great on the Monza so I should at the very least be able to get the bike to rev. But nope.

02-04-2016, 09:06 PM
After chatting with Ed we decided to get a new top end for Mike's bike. We ended up going with the Gila kit. Mostly because it was what Benji had in stock. It's a good kit. I've installed them for people previously with good results. I also picked up an OMG hi flow petcock, a new Top wrist pin bearing, high flow fuel line, and some new super soft Domino grips. This bike is getting some nice action. ;)



02-05-2016, 04:59 AM
Ordinarily I'd take like a week to get the exhaust port all polished up, but I don't have the luxury with this one since we want to go to the track this weekend. So I worked on it for most of the day, and night. I was able to remove most of the casting lines. Would have liked to drop down a few grits to get it highly polished. For not it's at least smooth. It's not bad--much better than stock. ;)



02-05-2016, 10:31 PM
I was all set to hear this engine spark to life today when I discovered something really cool, and yet it meant I wasn't going to be able to button it all up today. Popping the tope end off showed me that it was a 50cc kit. Pulling the piston showed me that it had a Metrakit crank. That's awesome news, but the Metrakit crank uses a bigger bearing on the little end. This is a desirable mod to be sure, and a great thing for this little engine. But it meant I had to race down to Treats to get a proper wrist pin bearing. First world problems I know! :lol: I did make it, and tomorrow I hope to hear some beautiful two stroke music. ;)

This hose was a bugger to remove. I had to use all my tricks! Okay I didn't put the heat gun on it, but I was close. :eek:


Inside everything looked pretty good. I'm really surprised that it had such low compression. Maybe with a proper ring it will do better, but then again as a 50cc barrel Mike would want to replace it anyway.




I didn't get a photo of the crank yet. Once I realized what it was I had to pack everything up and jump on the Silver bike. I'll probably get a nice photo tomorrow. ;)

For now here are some comparison photos.




Now check this out. These are the instructions that come with the Gila kit. Do people really do this? Crazy!!! :eek:

Derbi Motor Plaag, To install the conversion kit Derbi-Piaggio engines must check that the piston does not touch the lower crankcase, if so must be lowered in front of the crankcase, a diameter of 50 meters and a depth of 9 mm, with a special cutter for aluminum without disassembling the motor. Protect the stork blow and wash the crankcase to remove all the chips and check before riding.


02-06-2016, 06:20 AM
Now check this out. These are the instructions that come with the Gila kit. Do people really do this? Crazy!!! :eek:

Here's a technique I have employed in the past when in a pinch ...


Yes, Barbasol !!!
The foam keeps the little metal shavings of death from getting into every little nook and cranny.
You can then go and ShopVac out the metal shavings that have been magically suspended in the foam.
Of course, you will still need to thoroughly rinse out your work area.
This isn't a "silver bullet" and by no means the "proper" way to do the job, but in a pinch ...

02-07-2016, 02:30 AM
Wow today was a hard one. It was suppose to be a simple put the kit on, do some heat cycles, attend a few other things on MT Mike's bike, and wrap it up. Nope not even close. Xero I'm so happy you posted that hint. Some folks are totally against what I call Pickup Truck Mechanics, but when you don't have what you need you've got to Macgyver.

Here's the super nice Gila kit.


Proper bearing for the Metrakit crank.


Slipping the puppy on.


Quick look inside.


I actually then put the head on, torqued the nuts on the studs, and when to check the squish when klink. What? :eek: No way the crank would not turn around because the piston was hitting the bridge they put in there to stop the kids from putting kits on their street bikes. :(


Okay this meant a trip to the dollar store to get supplies. It also meant that I had to pack up everything to go to the store. Life without a garage in the big city. ¯ \_(ツ)_/¯

So first I installed the nice new high flow petcock and fuel line.


Well the dollar store had extension cables to get power for the rotary tool and shop vac to the bike--I bought five of them. But they didn't have any shaving foam. I knew I had some at home so I figured I just have to give it a better look see. When I finally figured out in which container they were stored I realize there was no way I would be able to dig it out. So off to get some. At the Walgreens I saw this:


The setup--a rag to keep particles from going everywhere. Q-Tips placed in the bearing lube holes. The hose from the shop vac that I would have running the whole time. Paper towel stuck into the cases (this worked really well when I put some foam in first). Then I would fill it up with foam.





It's pretty amazing how well it worked. When the rotary tool would catch the paper towel it would rip it to shreds spewing it everywhere. This actually happened a bunch. The first bit I use was way to dull, and didn't work too well. The second bit was nice and sharp, and things went pretty swimmingly afterwards. It's much harder to do this stuff with the studs in place. Well it's much harder to do this stuff with the engine in the bike. Damn. But it came out pretty nice all things considered.


Then a quick test to make sure there was enough room.


Putting the puppy in place.


Then a quick inspection, and what the hell? That's way too much gap.


And way too low for the BDC check too. What the hell? :eek:


I then realized this must be a Metrakit 43mm stroked crank. This top end wasn't going to work with this crank. And it was getting dark. I use to have one of these cranks. I gave it to someone that I thought would appreciate it (he didn't by the way). Some time later I happened upon a Parmakit 43mm kit. It's a monster kit and totally brand new. Well dig dig dig through the containers. Found it.



A quick check of BDC, and TDC, and it looked pretty good. This might actually work.



02-07-2016, 02:37 AM
Put it all together, torque it down and check the squish. It just barely had a usable squish. So I had to test it. I didn't bother with the pipe, water, or anything. Just had to see if it was going to run. Sure enough it started right up! Cool! :)



Then it was time to attend things like the pipe. Only to find that one of the exhaust bolt holes was buggered. Time for the thread chaser. These are kind of like taps, but they wont weaken threads already in play, which a tap would actual do. This was a bit of a painful process as my hands were already totally worn out from today's activities. I've still not really recovered from the crash, and the pain while always present gets pretty bad when doing work. And by this time I'm in some serious ouchy land.


Once the exhaust manifold was in place it was time to do the leak test. Well it wasn't holding so I got out the bubbles. Up sure enough right at the exhaust. I was going to have to get aggressive with some sealant.


Once that was happening, and the water all together, it was time for a heat cycle. The bike started right up. Smoked like crazy from all the building grease I used all over the place. But it sounded great. Revved very nicely, and seems to be doing well. I've since done a second heat cycle, things look pretty good. It's too late to do a proper revving of the bike now so the third heat cycle will have to wait until morning. ;)


02-08-2016, 01:40 AM
Today we went to the track. But Mikes bikes wasn't ready before we got there. We still had to fit different forks, bleed the front brake, add a new Res to the front brake, and tune the carb. All of this took me most of the day. Oh well. Didn't get much in the way of photos either. ¯ \_(ツ)_/¯

Lets start with the forks. Mike really liked how they were working. Once we got back I took a look at them. The left one seems to have leaked a bit, but the right one seemed to be okay. We will have to do some more testing. ;)





The drive out to the track was beautiful.





It was time to work on my Track Bike. There wasn't much time left so I only got to tend to the reed. As you can see the old ones were tattered. The Malossi reeds look quite nice. ;) And they worked nice too.




Pretty bikes. :)


02-08-2016, 08:28 AM
do you think that track is too tight for my 125 bikes tora?

02-08-2016, 12:34 PM
There was a cat out there yesterday running a Honda RS125. It was hella fast. Speedy says that you can do it, but you have to gear it way down. But were you to race they would probably put you up against bikes like the Moriwaki, and Honda RS bikes.

02-08-2016, 06:16 PM
Is that one of those 'fancy' Nology plug wires on Mike's bike ?
I assume it works well ?

Any line on a high flow petcock for a RS50 tank ?

02-08-2016, 10:07 PM
Yeah that is a Nology--I really hate that thing! It's such a pain to work around it. Things are already tight enough in there!

So you can sell you RS and get a Derbi!!! :P JK ;) Yeah I really haven't seen a high flow petcock for the classic RS, but I remember that Matt came up with a solution for it. Maybe from a KTM or something. Sorry that I don't remember what it was. :|

02-08-2016, 11:43 PM
Yamaha blaster petcock

02-09-2016, 11:40 PM
Well then here's one! The Pingell Power Flow (http://www.amazon.com/gp/product/B000WJ30L0/ref=pd_lpo_sbs_dp_ss_1?pf_rd_p=1944687582&pf_rd_s=lpo-top-stripe-1&pf_rd_t=201&pf_rd_i=B000GUWQK6&pf_rd_m=ATVPDKIKX0DER&pf_rd_r=1RBCW4VRZSFJK8M6SXVD).


Thanks Matt! ;)

02-10-2016, 12:23 AM
Thanks, indeed !!
I've had several cases where I have been running (60 - 65MPH, 11 - 12KRPM, 6 gear) on a VERY controlled bit of freeway near my house, and the bike craps out, with symptoms of a piston squeak (sputtersputter / dead)
Coast to a stop (~100 yards) and bike restarts, no issues. Subsequent inspections (compression test, visual inspection of piston / cylinder via exhaust port) show no issues.
Only thing I can come up with is lack of fuel in the float bowl, or some kind of wanky issue with the ignition.

02-10-2016, 01:16 AM
yep it has happened to me

02-12-2016, 12:09 AM
Found another one today, and since we've been going over them in this thread I figured I should post it here. Maxiscoot has a Bairikit Racing Digital CDI Unit (http://www.maxiscoot.com/brk-boitier-cdi-digital-racing-brk-cdi-02.html) that features variable timing. Now the pricing is high enough that you might as well get an HPI with a smaller flywheel, but if you want to keep the Ducati stator and flywheel here's another option. ;)

I've looked for a graph of the curve, but I've not been able to find it. :eek:

It does come with that cool Domino switch I wrote about recently (http://www.apriliaforum.com/forums/showthread.php?275584-Derbi-The-Red-Power&p=4001954&viewfull=1#post4001954). ;)

BRK (Barikit Racing Kit) CDI unit, digital racing version (with variable ignition timing), compatible with original ignitions. Note - make sure you order the right version for your ignition. Simply swap with OEM unit.
For Ducati ignition.


02-22-2016, 12:18 AM
Hi, do you know brand and part number of the aftermarket fuel petcock for the rs50 ? Thanks

02-22-2016, 12:59 AM
The link in ToraTora's post goes directly to the part being sold on Amazon. That's where I bought mine from ...

That being said, I haven't installed it yet, so I cannot vouch for it directly -
Nice part, tho !

02-24-2016, 03:22 AM
Hey Cats, well we got to do a bit of work on MT Mikes track bike today. I pulled the top end to check on it since when I put it together I didn't have the time to do all the things I normally would do--like properly chamfer the ports. As you can see there is a bit of scoring on the cylinder.





Another thing we wanted to get to was the fork leak. We picked up the Motion Pro fork seal cleaner, but ran out of time. We'll have to try it out net time.



Mike painted up the plastic bits in white.



02-24-2016, 10:26 AM
The tank fairing looks awesome in white!

02-24-2016, 10:29 AM
Tora, would you post a picture of a really well chamfered cylinder?

02-24-2016, 02:38 PM
From my The Red Power thread (http://www.apriliaforum.com/forums/showthread.php?275584-Derbi-The-Red-Power&p=4003560&viewfull=1#post4003560)...


04-13-2016, 04:04 PM
So it seems that the AllBalls seals aren't a good enough fit for the newer GPR forks. So all of the Second Edition GPRs do have to have that off sized seal. I've got some coming from EZ Parts. Once that's going on MT Mike's bike should be in good shape. He picked up some jets, and the next time we get to the track we'll do some fine tuning. ;)

06-18-2016, 12:41 AM
It's been a while since I've done some track bike action. Today I headed over to MT Mike's place to get his bike into shape. Had to get the fork seals done, put on some plastics, test for leaks, and basically give it a once over. Everything went well. I also picked up my track bike for some wrenching action, but ran out of time to get any done today. :P









06-25-2016, 10:02 PM
It's nice to be able to get some good wrenching in on this one. :) A couple of days ago I got the petcock switched out. This one is much nicer. I only have half of the new tubing I needed for it, but that's better than none. :eek:



One of the things I really needed to attend to was swapping out the silencer. I had the really nice JollyMoto on the bike and it would totally suck to mess it up with a low slide.


To replace it I had this beat up MetraKit silencer that would do just dandy, but it's much heavier than the Jolly (which is why the Jolly was still on the bike).


This meant that my temp fabrication binding strap solution would no longer be acceptable, and therefore had to go. I had always planed on doing this work, just never had the time to get to it. :eek:



Had to clean up the pipe and silencer a bit, and the copper coat them.



Replacement of the lower support unit.



Connecting the silencer.


I also did a bit of work on the rear brake lever since it had gotten loose again. Got it all adjusted and cleaned up. :)

Next it was time to get to the fabrication. This is super heavy with photos so I'm doing to do it in another post...

06-25-2016, 10:29 PM
I kind of knew what I wanted, but since I don't have access to a workshop these days I pretty much had to wing it. It came out about what I wanted, and I'm mostly happy with it. The bends could have been better, but considering I don't have anything close to the proper tools they came out great. :lol: I figured some folks might want to know how to make these so I took a lot of photos to help understand the process of how to fabricate something (on the fly).

I had a big chunk of aluminum sheet scrap with which to work. Holding it up to the bike I could get an idea of what I wanted.


First I drilled a proper size hole in it as a reference. You have to start somewhere. :P


With the hole in place I employed some green painters tape for a cut line, and then cut it with a jig saw. It wasn't as straight as I would have liked, but I'd be able to clean it up with the file.





Checking out the fitting, and measured for the next hole.


With the second hole in place it was time to mark the top cut. I would have to cut this left handed because it's really difficult to get a good cut started on such an angle. Then I added a nice radius to the corners with the file.




With it in place I could figure out where the first bend would go. I decided to make the bends parallel to the frame of the bike.




To achieve the bends I used a chisel to mark the crease. Then used a couple of wood blocks, and some hand force to make a bend.



Same thing for the second bend.



The bottom needed a bit of trimming, and a bit of radius to the corners. After which a quick sighting for the final hole marked with a Sharpe.


Then clean things up with the file, and put it all together.





06-25-2016, 11:40 PM
Nice work !!

06-26-2016, 02:19 AM
Looks great!!

07-01-2016, 09:09 PM
Yesterday I was working on the chain when I noticed that the bottom roller was missing.


Digging through the boxes today I found some roller parts.


After cleaning things up, using some new stainless washers and nylock nut things started looking the way they should.



With the chain replaced--I did this yesterday. The chain on the bike showed way too much stretch, and I had this chain from the Black bike that was in good shape, but a bit dirty. So I cleaned it up, and fitted it to the track bike. I also dropped the front sprocket down one tooth. I would have probably had gone down another but I didn't have a 13 hanging around. But to go to a 13 would require getting a different chain, or pulling some links.


Another thing I'm looking into is a way to protect the frame if the bike goes down. This super ugly tail section is hanging around so I might clean it up and employ it.




07-24-2016, 08:03 PM
Technically evolution happens within a population and not on an individual. :lol: So it's not the correct word in this case, and what I really mean is gradual refinement. I finally got the new brake reservoirs fitted to the track bike. I still need to work on the mount for the front, and I'd really like to replace the hose for both of them, but this will do for now. ;)

These are the units I ordered from China on eBay. They are nice enough, but they do come all scratched up because the put the hardware in the same bag an the reservoirs. It's a shame because you can't order these for any project that you want to look nice. :( In this case I suppose it's okay because a track bike is one where you expect to crash. :eek:


I'm replacing the stock rear, and the nice Procircuit unit from the Red bike that's been on the Track bike for a while now.



And the new Chinese brand units installed. :)




While doing this swap I noticed that the front brake felt a bit soft. So I did a quick bleed job on it. Now I'm thinking that the Brembo I have fitted on this bike is way too much master. It's the 16x18 track master. It's very nice, but on this bike with it properly bled it feels rock hard. Very little modulation. I'm going to have to source a different master for this bike too.

07-28-2016, 06:19 PM
The leads from the kill switch on the Track bike were of a different type than what was available on the bike. The lead to the CDI unit happened to be the same which was nice, but the lead to ground needed a proper connecter to the bike. Today I had a moment to fashion up a short adaptor wire. Sadly I've run out of appropriate heat shrink tube and had to improvise with the old fashion method of electrician's tape. :lol:




12-10-2016, 10:26 PM
We went up to Sonoma for some circuit riding. The White bike it MT Mike's, and the Black bike is mine.










12-10-2016, 10:40 PM
The Reese Jupiter shock fitted to this bike (thanks to Owen!) has a remote res. I needed to come up with a better mounting system for it. I took some inspiration from the silencer mount that I had previously made for the bike.


















01-12-2017, 11:31 PM
Found a really old photo of the Track bike before it was the Track bike. ;)

I think every single part on it has been swapped out. :eek:

http://i1064.photobucket.com/albums/u365/derbigpr/bikes/Derbi%20Track%20Bike/Derbi%20GPR%20Track%20bike%20Before%20Mod_zpsrn14b y0i.jpg

01-29-2017, 02:22 AM
A little discovery...



02-03-2017, 09:24 AM
New project bike? I'm sure if anyone can bring that back to life it would be you!

02-09-2017, 11:30 PM
I'm collecting bits for the next GPR Camp build fest. Picked up another one on Sunday. So much work to do! lolz

02-13-2017, 11:46 PM
I've been talking about these bikes for quite a while--an American made two stroke (http://cobramoto.com)! Yes you can actually buy a brand new two stroke motorcycle made in the States. Currently they only make dirt bikes, but I really hope they start making circuit bikes, and this is one of my motivations for getting a Cobra over the other options. One of the trends at the track is to take a 65cc dirt bike and set them up for Mini Moto. Most folks get a KX65, but some do get the 65SX. Both are nice bikes. The KX is generally less money, and the KTM is more, but I didn't want to go with either one since there was an even better option!

The Cobra CX65
Cobra started in 1993 and are based in Michigan. They are focused mainly on race ready PeeWee moto crossers. They basically build a works bike that can run in the stock class. Because they already come with all the bling they have a huge advantage over the Japanese and Euro bikes. For those bikes if you set them up with the same gear they wouldn't be stock, and thus would have to race in a different class. For this reason Cobra just totally dominates the PeeWee classes from entry level 50cc to 65cc.

These bikes are truly amazing with custom parts everywhere. Even the frame is made of custom high carbon steal rolled into oval tubes specifically for Cobra. The cases look like they are billet. The bike is incredibly fast--and I may have to detune it for the KSB drills (http://ksbsport.es) that I want to run. Still it is an awesome bike that's way better than the competition--and yes Virgina it has a power valve. ;)

The one I picked up is a 2013 model. It raced for about three seasons, and won quite a few races. :) I'll need to do a bunch of set up on it, and replace a few parts here and there. I also intend to get some sliders, and change out the wheels. I may lace up some proper sized rims to the stock hubs, or I may just get some mags for it. I'd like to get the mags because then I don't have to deal with tubes. lolz The Mini Moto guys have worked out most of the mods for the other brands so it's just a matter of adapting the knowledge.

The Micky Dee's color combo is a bit off putting, but they do sell the plastics in all black, or all white, and I'm quite grateful for that option. lolz Yes, I will take fries with that...







03-09-2017, 01:59 PM
Just got this link from Scotty Dog! Oh my is this cool. Now the newer versions of the Euro3 come with this built in, but the early ones don't have it, and the Euro 2s never had it either. MetraKit did make something like this, and I have one installed on the 45mm stroke engine. This is a really nice upgrade!


Google translation:

In 50cc with box the Derbi engines are reputed to be the best performers. However, they still have a weakness in the transmission when one starts to have a motor a little more advanced. In fact, the clutch bell pinion undergoes high pressures and the friction with the ring creates a deformation of the latter. As a result the bell remains blocked with the box shaft. This type of mounting on a needle cage thus prevents friction and therefore wear on the ring. Derbi has been aware of this problem and since 2014 they also use this type of assembly in original equipment. The Racing clutch bell gear has needle cages of 20x26x12 for high resistance.


03-09-2017, 03:01 PM
Just got this link from Scotty Dog! Oh my is this cool.

cheers Tora! Was a lucky find as I have been on that site many times and not noticed it. I got lucky recently to have found old stock with the Metrakit version, but it's totally awesome to have this available and makes me comfortable as a Euro 2 fan!

03-23-2017, 09:40 PM
Some bits showed up today. :p:


03-24-2017, 01:43 AM
Is this for GPR camp ?

03-24-2017, 12:22 PM
Is this for GPR camp ?

These parts are for the Cobra, which I'm setting up for doing drills, but will also have a mode (by doing a carb change) to take out on the kart track. It's a really fast bike, so I need to restrict it for doing drills. But on the track having moarrr powaaa is well, fun. ;)

I'm probably going to bring the Cobra to the camp site though since there's a huge parking lot, and a long private driveway. I'm really looking forward to having some fun there.

I do have, and will be ordering more bits for the GPRs. I think lots of folks are doing EasyParts, and MaxiScoot orders. Another good one is Scoot Fast (https://www.scootfast.net) (like in the previous post). They have a bunch of neat bits I've not seen on the other sites.

Oh and Easy just did a facelift on their site!

03-31-2017, 01:05 PM



04-02-2017, 12:21 AM
After some cleaning the hub was ready to lace up. The directions for lacing the wheels were pretty interest, and figured some of you might like to read them. The bummer came when I started to true it up and discovered that the spoke wrench doesn't fit the new nipples. ¯\_(ツ)_/¯ Gotta get another wrench. :/

Still it's going to be sexy when it all comes together. :)







04-02-2017, 11:19 PM
It was a long weekend of the wrench!













04-08-2017, 09:02 PM
Today was remove the suspension from the bike day. I'm getting custom springs, and the forks are going to have lots of new bits put in. Seals, and bushings, and such. To remove the shock I ended up taking all the plastics off. Those are getting replaced anyway, and since it would make it easier to remove the shock why not? lolz

I also removed the rear wheel, and then proceeded to remove the hub. The spokes with the kit are of different sizes, so I need to check on that before going forward. The stock spokes are all the same size.

The steering bumpers seem to be missing! Have to look into that one.

The rear hub is one sexy piece of art. Reminds me of some of the BMX hubs we use to sport.










04-11-2017, 01:59 PM
I'm considering running the Cobra in two modes. Drills mode, and track mode. The only real difference will be the carburetor fitted to the bike. For the drills very little power is needed, but on the track it would be nice to access that power. The idea is to set up low power mode with one of the 17.5 PHVA carbs I have laying around from the GPRs. If it's too much I could even use a 14mm PHVA.

One of the issues to solve with this plan is dealing with the different pull lengths of the cable. The 26mm carb will need more pull than the smaller carbs. ODI makes a motocross grip set that comes with a throttle tube. This tube has removable cams. The grips come with three cams, and there are others that can be purchased too. Simply by swapping cams the amount of twist on the grip will remain the same, but the pull length will be adjusted for each carb.

Another neat feature is the left hand doesn't require any glue or wackiness for installations. It has a locking mechanism that allows it to be attached to the bar. There are also many color combinations, and some various grip styles. Near as I can tell they are all closed ended so if the bike has bark busters, or bar ends the ends of the grips will have to be opened to accommodate.

Now for the good reader paying attention this system's advantages come to light in that most of the 1/4 turn throttles out there pull way too much for the tiny carbs run on the Replicas. Swap out this throttle tube, and select an appropriate cam, and you can have a 1/4 pull throttle that actually turns a full 1/4!


04-16-2017, 01:32 AM
Laced up the rear wheel. Still waiting on the proper spoke wrench to finish these up. The one that came with the kits is too large and rounds out the nipples. :(

The suspension is next. It's all coming together with this one--slowly, but it's on the way.




04-19-2017, 02:24 AM
The Track bike is currently fitted with the HPI mini rotor. This is a great ignition, but it does't have an accessories circuit, and the one that they sell for it is a total piece of garbage. Since the track bike is going back on the road for GPR Camp I need to fit it with a different ignition. But once you have a variable curve you just can't go back to a static curve. The solution? Well there were a number of them, but what did they have in stock at Treats (https://www.treatland.tv/ProductDetails.asp?ProductCode=TOP%2Dperformance%2 Dbox%2D9921690)? The Top Performances 9921690 Red Box.


Now most things you will read for this unit state that it's for the AM6, but that is qualified by Top when they say AM6 type engines. Well that's good enough for me, and when you consider that the Red box is designed for the Top performance top ends (yeah I know that's a bit hard to parse!), that the Derbi employs the same Ducati ignitions, and some of the CDI units sold for these bikes are marketed to both bikes I figured this should work. And if it doesn't them maybe I'll have to get another RS50 down the line. :lol:


In all the photos I've ever seen of this unit I've not seen the back of it--which is just a potted box with wires coming out. Not so clean looking compared to most CDI units. It's actually kind of shoddy looking considering how expensive this unit is compared to other units. I'm going to have to fab up a mounting bracket since the older GPRs really aren't set up for this sort of thing. It actually would be pretty easy to mount this in the 2005 because that is set up better for a two part system. The HPI unit comes with a bracket for the coil, but the Top doesn't.


Some of you are probably wondering why I didn't just get an HPI 2Ten for this bike since I'm running them on some of the other bikes. Part of the reason is that I've never (and yeah I mean never) gotten a 2Ten to run correctly, or satisfactorily, and the other reason is when I did try to get one for this bike they didn't have any in red. The gold ones look way to garish, and the black ones, well I suppose that would have been okay, but really I wanted a red one. I still make install a 2Ten later down the line when they have red ones, and then maybe move this unit to another bike.


There is one advantage of using the Top unit over most other vectors and that is you would still be able to use the electric start since the Top unit employs the Ducati stator and flywheel. Still there are caveats. I can't seem to find it tonight, but I remember reading that this unit doesn't work with stroked cranks (http://www.twostroke.se/product.asp?product=22960). So if you don't have the 40mm crank in the engine you may not get away with using this CDI. I don't know why that is, and that's something for me to research in the future, and the future is now.

Unrestricted digital CDI with variable ignition point

CDI box with ignition coil from the Peak Performance with variable ignition point.

A brilliant product for anyone who wants to upgrade his bike and does not want to replace the entire ignition system, and keep the ignition is set manually.

The CDI box has been designed for the Minarelli AM6 engine that has the 6-spoliga Ducati ignition plate, but also works with the Derbi ignitions which have the 6-spoliga Ducati ignition plate.

When the original CDI has the same ignition point through the entire registry to have Peak Performance have developed this product which has an internal microprocessor which allows the spark advance is adjusted automatically, the more revolutions the motor has, thus optimizing the ignition point.

The CDI also has a very good lighting control called "Power Control", which ensures that pre-ignition is prevented, resulting in that you get a cleaner ignition.

The ignition control also ensures that you get a longer life for both ignition systems and spark plugs.

The other major advantage is that fuel consumption is reduced and this also includes air pollution.

This kit contains the following:
1 st - CDI
1 st - Ignition coil with 5 kOhm primer + cable
4x - Kardborrebitar for mounting

NOTE! This product is intended to be combined with Top Performance 70-75cc cylinderkit in their Redline series but can also be combined with equivalent cylinderkit.

IMPORTANT NOTE! This CDI kit is not intended to be used with the kits in 85cc class, or cylinderkit with extended stroke as this can cause damage to the ignition, and the cylinder to seize.


While the directions come in a metric shit ton of languages reminiscent of a Japanese pocket radio, or shaver, there is nothing about the actual ignition curve for this unit. This kind of, no this totally sucks with regards to tuning the bike. I guess they just want to to bolt it on and go. The only method one would have to adjust it would be to run the flywheel without the woodruff key and adjust it from there. This is basically what you do with the HPI units, and of course the stator plate has a small amount of adjustment. But since you don't know the curve the only way to know is to put a timing light on the unit, and most timing lights don't track at 10K plus RPMs. Pain in the ass desu.


And of course if you go searching the web for information about this unit you end up finding what I've already posted (http://www.apriliaforum.com/forums/showthread.php?313352-Ignition-Alternatives-for-Ducati-CDI-on-AM6-and-GPR-engines). lolz

However, the clever cats at RRD (http://www.rrd-preparation.com/en/wind-high-tension-replacement-lighting-minarelli-am6/948-kit-preparation-allumage-origine-ducati-bobine-haute-tension-cdi-top-performances-racing-tpr-minarelli-am6.html) have posted some information that points to the answers:

This kit is intended for engines minarelli am6 equipped with a lighting of origin DUCATI, following our tests, laying on DERBI not hurt anything! The power gain feels from 7600 rpm and this kit allows blithely exceed 16,000 rounds against a clamping or malfunction 11 000 see 13,200 rounds of ignition source according bikes, this kit really allows full advantage of the large kits , their powers and their times. for this plant, TOP PERFORMANCES has developed a curve and special mapping to make the most of the engine power especially at high speeds. The CDI unit has a microprocessor on which the mapping is stored, this allows for a modified spark advance according to the variation and the number of engine revolutions.

The advance self shifts backward to the couple and low speed forward has high revs so that the engine can take endless towers .... A huge power won face a fixed beforehand, the fixed advance does not allow you the maximum power for the spark always come at the same time (advance remains the same) despite the number of revolutions per minute, however an engine demand more or less in advance by his regime. In addition, TOP PERFORMANCES has still pushed further this pack by opting for a high ignition coil separate and reduced voltage, this offers less ignition heaters, improved mass and an additional power spark. The high-voltage wire in the Box is a high-end cable, more TOP PERFORMANCES added parasite competition without resistance. What have a really powerful and ultra strong ignition, torque gain is really felt and gain high / midrange is amazing!

Remember, once the kit installed, use only gasoline SP98! More SP95 which could generate rattling! This pack is not to be used with the kits TOP PERFORMANCES 85cc and 86cc without removing the staggered wedge ... At high speeds you would too far ahead, this will create overheating and tightening risks. A beautiful pack of variable advance TOP PERFORMANCES RACING.

I also found this graph for the Top Performances 9909300 CDI unit that can be fitted to older RS50 machines.



04-19-2017, 06:11 PM
I really dig the added performance from my Red Box CDI.
Also liking the extra tech you managed to dig up on it, consider it saved.
RS_Patrick posed this awhile ago, I have not had the time to verify it.
Maybe you can ...


Would like to get your feedback on your experience with this CDI once fitted.
Top also sells an Offset Key (6 or 7 degrees), wondering if it is the "special one"?

04-19-2017, 06:34 PM
Thanks for that image.

Here's what the Goog translator had to say:

Ducati ignition generator from Rieju 500 to the impeller 31 10 1210 BF It is measured with a Ducati 323 990 10 99 7 ignition switch. The charging capacitor has 2.0HF, the displacement curve is based on a reference setting of the Zzp, at 7000 rpm.

engine rpm
charging charge
ignitions charging
current charging
energy to adjustment.
Speed ​​voltage per spark per sec.
Average M value per second at 7000 rpm

I also sent off an email to Top for more information. I'll keep you apprised.

04-20-2017, 06:48 AM
I am curious to by it can't be used with stroked crankshaft. I wonder if the curve is just shifted more advanced to suit higher rpm engines so would cause an issue for the stroked ones? But the thing is stroked engines naturally retard the timing so you need to advance anyhow. I'll leave Tora to be the guinea pig!! lol

04-20-2017, 10:48 AM
This morning I received an email from Top with this graph:

Top Performances "Red Box" 9921690

http://i1064.photobucket.com/albums/u365/derbigpr/bikes/Derbi%20Track%20Bike/Top%20Performances%20CDI%209921690%20AM6_zpstmebfp cj.jpg

HPI 2Ten


Xero how does this compare with your experience? It doesn't seem to correlate very well with what Patrick posted. I'm really surprised by how long it takes to kick in. And it's very different than the HPI 2Ten curve.

Thanks Scott!!! lolz

This will be interesting. I probably wouldn't have bought it had I seen this graph because it's in the ranges of 7K to 10K that I really want to see a performance chance. With the HPI by the time it's at 11K it is already well past the max of the Red Box. And the Red Box really doesn't do anything until 10.5K!

We should also probably try to find out where the stock ignition stabilizes. If it's around 20° this wouldn't feel much different, but if it's around 25° then there would be a small change. Moving the start point with either a special, or modded Woodruff, or just moving the flywheel without a key is an option, but since the variation pretty much occurs within 1.5K (plus another 2Kish) worth of RPM the change would need to be precise.

04-20-2017, 12:11 PM
Wow, Great info on the red box! I have had one of these sitting in a box somewhere, Hopefully I can still find it, and eventually plan on installing on my RS$10k.

04-20-2017, 03:41 PM
jesus christ that is a lot of goddamn timing

04-20-2017, 06:06 PM
jesus christ that is a lot of goddamn timing

I could add some 4 letter words to that, but I think Matt summed it up right there !!!

I really would question that graph from Top (I could be wrong though).
That is almost completely counter to typical 2 Stroke timing.
I wouldn't have guessed from my "butt dyno" that it was so FLAT for so long, with such a sharp drop.

My impression starts with the fact that my RS wouldn't rev much past 10.5k no matter what I did (go-fast goodies).
This was my initial take on it ...

With the carb set-up and running rather well I figured it would be a good time to mess around with this CDI and see if there is a noticeable difference.
I left the OEM CDI in place so I could quickly swap back and forth between the two CDI's.
First thing I should note is that when I got my '01 RS50 the engine, intake, exhaust was 100% stock.
The bike would only rev to 10500, that was it. It would run right up and stop, wall ...
(Of course freight training down a steep hill would push it past)
Missed shifts at the wall would still only over-rev to 11250.
(My AM6 trans finds a neutral between 5th and 6th all the time and likes to pop out of 6th into neutral when hitting heavy bumps. Only 6th though)
After fitting:
Dellorto 21mm PHBG Racing carb,
V-Force Reed Cage,
Leo Vince V6 exhaust,
AF1 air filter for OEM air box,
and all the custom trick "wastes of time" to make it fit the bike would still only rev to 10500.
It got there a lot faster and all that but still the wall remained !!!
I ran a couple quick warm-up laps around the back roads and swapped over to the TOP's CDI and took it right back out.
The wall had been smashed, ran over, and was now only visible in the mirrors !!!
Instant 11500 and 12000+ easy in down hill over-rev.
5th - 6th miss shift neutral sends needle blazing well past 12000 instantly (caution needed here for sure on a stock crank).
So there you have it ...
My CDI in my bike had some form of restriction built into it.
Was this restriction just an unintentional "by product" of poor ignition timing ...
Or was the poor ignition timing an intentional act of restriction ???

I have since dialed the Carb in even better and done some other minor tweeks and my RS gladly rev's well past the 12k on the Tach.
I would say good output starts around 9k, power feels rather light below but rev's quick and steady to the 9k.
Nothing like the "dead holes" of other (race oriented) 125/250 2T's I've had the privilege of ripping.
Power starts to fade out around 11.5 and somewhere a little past the 12k mark it feels like it starts "missing" and then output really drops.
The Power Band does feel rather flat, so that would at least follow suit with Top's graph in that RPM range.
The "missing" could also kinda jive as well, my issue might be with fueling tailored to work with their timing of the RED Box at normal (street) engine speeds.

This is all very interesting !!!

Thinking back on it, I believe the chart Patrick posted was the Stock timing for the Ducati Ignition on the RS, not the RED Box.
Might have to Plot that against the Top and HPI graphs.

Oh, I think the "Black Ones" are just fine ...


I can almost feel the headache this is going to cause already ...

04-20-2017, 10:12 PM
i would not run that with less than 110 octane

04-22-2017, 09:32 PM
The wrench that came with the rims and spokes was rounding out the new nipples. Here's why:



05-01-2017, 10:38 PM
The Track bike's conversion continues. Ed hooked me up with a tire swap today. Even put in new valve stems! Ed ROCKS!


05-15-2017, 12:22 AM
Today was a Wheel day! Yup. Cleaned up both wheels, removed the front disc, dressed the threads, and installed the new NG disc. It's really important to heat up the bolts before you try to remove them, or they will break! :eek:

Yes this isn't the stock rotor, but it's very similar. The main difference is the fasteners. With those switched the disc works fine. It's the same stats as the stock one, but with the newer look that came out for the 2005 machines. There is one difference, the stock disc is .5mm wider. It really shouldn't make much difference. Make sure you employ the proper thread lock!













05-15-2017, 08:24 PM
Nice little Dutch surprise showed up today...

There's actually stuff here for many different bikes, including the radiator for the Black bike. But many of these things will go on the track bike so it's good. :)



05-23-2017, 10:48 PM
Hard to see in this photo but the right hand switch arrived. It's the same fancy one I put on the Black bike. Should make it easy to set up a few things on this bike. ;)


06-09-2017, 12:38 AM
Lots of effort went into this bike to get it converted back to street for GPR Camp. Both Jimmy and Ed helped a lot, and with their awesome help I was able to get the bike ready to ride. There were a lot of trials and tribulations solving all sorts of problems with the conversion. I had to borrow, and scrounge parts from many of my other bikes to pull it off, and come up with some creative solutions. Most of which I'm not even going to bother to document because they were just too crazy. It was worth it though because I'm really happy with how the bike looks and how it's running.

The custom shock res mount, and exhaust hanger needed to be modified for the tail section to fit. The shock res mount is a temporary mod because I didn't have time to do it properly. There was just to much to accomplish in too little of time.



Another big thing to get done was the ignition. First I had to take off the HPI, and because I had to move the bike stuff I couldn't find the puller. I was under extreme time pressure so I had to resort the Pickup Truck mechanic's method--which worked great. Then I had to come up with a mounting system for the Top. I used part of the HPI coil mount to mount the Top coil, and zip ties to mount the CDI.

The wiring was pretty straight forward. Just like the stock CDI really. The White/Black cable connects to the Green/Black cable to kill the engine. The top end on the bike is the Project Poor Man's ProRace (the modified Airsal I did some years ago), with a MetraKit ProRace pipe, and a 24mm MetraKit PWK carb.




The Mychron 3 ended up being great, and unfortunately I don't have photos of all the work that went into putting it on the bike. The one photo I took is the speed sensor which required a magnet. I ended up using one pulled from the fridge! lolz Ed fashioned up a bracket for the sensor, and then I wired it up. The Mychron 3 has two temp sensors, a speed sensor, and a tach sensor. It can also sense a beacon on the track, but I'm not employing that for it. It records the data which can then be fed into a computer and analyzed. That's something I might play around with later. It also features warnings for low temp, and high temp for each sensor, tach limit, and I think it can even figure out what gear the bike is in based on speed and RPM once setup. I've a bit of learning to do with it yet. lolz You can also seen the new rotor I found that would fit the bike.


Lots of work went into the livery, but I only have finished photos. These mostly came from at GPR Camp. ;) I got some nice bits from EasyParts including new mirrors, and clear blinkers which also give the bike a nice look. And it got a new set of MC18s--If you have one of these bikes and you don't have these tires yet I don't know what you are waiting for--these really make a huge difference on these bikes!










The chain is worn out, but I didn't have time to replace it. Will have to do that soon. I also need to get some Derbi stickers for the faux tank.

The bike runs really strong. It's got decent mid-range power, and when it gets on the pipe it pulls. The funny thing is how late it gets on the pipe--somewhere around 9500 RPM! It does seem to struggle from 8500 or so though. That 1,000 RPM is really tough to ride around, and I'm going to have to see if I can tune things a little bit better.

Ed's RS50 has the aluminum Top Performance kit that Matt set up. This bike can out pull Matt's kit by quite a bit. Which was a bit surprising--pleasantly so. If you can keep the bike on the pipe it's an absolute joy to ride. We had some spirited riding on Panoramic, Bo-Fax, and 21 corners and it was just so much fun. It was lots of work bringing this bike back to the street, and oh so worth it--now I'm going to have to give the bike a different name. ;)

06-10-2017, 10:46 PM
Impeccable, as always.

06-11-2017, 09:07 AM
that's awesome! what gearing and pipes did both bikes have? i has best luck with the moto carenzi pipe

06-11-2017, 11:56 AM
Gee, it can only be perfect!! I Love it!

06-11-2017, 02:16 PM
Impeccable, as always.

These are Hollywood photos. As long as you don't get too close. ;)

that's awesome! what gearing and pipes did both bikes have? i has best luck with the moto carenzi pipe

My bike has a lot of advantages over Ed's. I have a ProRace pipe, I think his has a Gianelli. I'm running a 24 Metrakit carb, he's got a 21 CP. His gearing is set for the freeway, mine was a bit lower. I'm running the Top CDI, and I think his is still stock. I have way better tires. ;) Still I was doing comparisons on when the bikes were both on the pipe and pulling strong. I think he could probably do a lot to get more performance, and I probably couldn't do much more. ;)

Gee, it can only be perfect!! I Love it!

Thanks--this is just a fun bike. I wanted it to at least be presentable for GPR Camp. And of course be fun to ride--which it was in spades.

06-11-2017, 08:22 PM
Here are the MyChron 3 Golds that I picked up. One of them is now installed on this bike. I need to post some photos of the installation. :P But for now you can see the boxes. The one I used has a mod to allow it to take power from the bike rather than wasting batteries. I've read that these should last months on a set of batteries, but this one wont even last a day on a new set. It also kills the bike's battery--even when turned off. For now I'm just unplugging it after riding it. I need to set the power to go through the key switch. :P


06-13-2017, 09:07 PM
Here are some shots of the MyChron3 Plus installed. The dash unit connects to an accessories box. The sensors plug into the box. There are five possible sensors. In the photo on the bottom is a wire loop--this is the sensor for the tachometer. Above that are the two temp sensors, speed sensor, and beacon sensor connectors. I've currently only got the speed sensor, and temp two connected. The temp one sensor connection will show up when I get the EGT sensor, and I may switch the CHT sensor for an H2O sensor. The beacon I wont be using.

The wires at the top are the power mod wires. These connect to a small 12 to 7.5volt convertor that is directly connected to the battery. I need to change this to feed off the key switched power. The MyChron will kill the poor Shirai lithium battery. The lid I had to use was one of the crashed up ones. I have a nicer lid for the unit, but I have to mod it to work with the external power mod.

To attach the box we used two self tapping screws set in a pair of pilot hole drilled into the dash mount. The bottom was secured with a zip tie. The dash is secured with one nylock nut.






06-26-2017, 12:12 PM
The sensor cabling for the EGT showed up today. Their hose clamp setup doesn't have an angled bung like the Koso/Stage 6. Seems like it would be more predisposed to leak. Because of that I think I'll have to braze this one on.


07-03-2017, 01:06 PM
Went out to Monterey on Sunday for some riding. Got in nearly 150 miles in the bike. It was running great--well until I broke the pipe! lolz I had to patch it up with sticks and zip ties.

I also stopped at the Tallbot Moto Museum. This is a must see for you folks. I got to hang out with Bob the curator at the museum. He came up to me because two stroke! We chatted for quite a bit about them. He use to sell Aprilias and Derbis and was familiar with the bikes. He also has a V4 Yammie stroker! I had just missed it--he had it there earlier in the morning. Oh well next time, right? He was working on a vintage MV which he rode around in the parking lot.

Basically this ended up being a scouting mission for a future ride. I learned a lot about the location, and found some great roads. I stopped at a gas station and a cat came up to me saying what a great day for riding. He asked me if I came out there often. I admitted this was my first time riding out there. He then spend a fair amount of time explaining to me where I could ride, the distances, rode types. It was awesome to gain this local knowledge from a fellow rider.

I had to use my phone as a navigator so it was zipped tide to the bike making it impossible to take my usual snaps--but I was able to capture some frames from the video. They don't look as good, and are ultra wide--which distorts, but you might be able to get the idea.


























07-03-2017, 01:17 PM
Lol, hilarious pipe repair.

07-05-2017, 11:51 AM
You have to get creative when you are out on the road. This is why it's important to have a bunch of zip ties with you!

07-30-2017, 09:05 PM
It's time to put something together for the track! Since the track bike was repurposed to the street for GPR Camp there's no longer an actual track bike. Before summer is over I really want to get some time in on the track.

I'm taking one of the track bikes I picked up in the spring and setting it up for track duty. Today was mostly sorting through the parts, and starting on cleaning. I have most of what I'll need, and hopefully wont have to grab too many new things to get a decent bike on the track.

The frame I'm going to employ could really some paint or powder coating, but if I go that route I wont have much time to ride. It kind of makes sense to do that at a later point in time.

The engine is likely to remain a stock 50cc top end. Eventually it might get a different top end, or it might need something sooner depending on the carb/intake situation.

Here are some photos.











08-01-2017, 10:20 AM
You certainly know how to do it Tora.
Wonderful pictures, thank you for that.
Its been too hot for the track lately.
even though they have evening practice, I'm too tired by then.

08-01-2017, 01:05 PM
You certainly know how to do it Tora.
Wonderful pictures, thank you for that.
Its been too hot for the track lately.
even though they have evening practice, I'm too tired by then.

Same here. 63 and working construction all day in the hot sun. Hard to get enough energy up for a late day ride!

08-01-2017, 02:40 PM
I feel ya brother.
13 years behind ya and if it keeps going like this 63 is going to be hard to take !
still better than the other option !
knees down !!!

08-03-2017, 09:13 PM

I had better expectations for this week, but so far no progress. Maybe tomorrow. :p:

08-04-2017, 08:13 AM
did you move ? that doesnt look like your place lol

08-04-2017, 12:42 PM
This year before GPR Camp I was forced to move all my moto parts to a storage. This took a huge amount of effort and destroyed my bike prep schedule. I actually gave up on building any of the bikes, and just focused on converting the Track bike to street. Not even a build really. Even then I didn't have enough time. It was pretty rough.

It was very much a SWATT move. Even though I tried to keep things organize lots of stuff is MIA. I'm pretty sure it's in there somewhere, but that somewhere is a challenge!

08-11-2017, 01:39 AM
Lots of progress on the New Track bike today. :)

Mostly it was sorting and cleaning parts, but hey that stuff is important. I'm basically going through the bins from the two track bikes I bought earlier this year, and combining them with some parts from the previous Track bike.


Got the rear wheel pretty much ready. I might be swapping out the rear sprocket though since I have some nice aluminum sprockets from one of the other bikes. But to get started this in fine. This is going to be a refinement process anyway. These wheels were on the previous Track bike. They are probably my nicest set of wheels though. If I had infinite time I'd move the tires around and save these for the Red bike.



Got the shock and linkage cleaned, lubed up, and in place.





Cleaned up the brakes. Wont have anything special this time around. The pads looked like they were brand new. Not sure what brand they are, but they will be fine for now. I'd like to upgrade the master, but again this will be fine for now.




The chain adjusters took forever to clean up. I like how the inside parts still say Cagiva. They ground the little elephants off the backing plates though. So sad. :(


And the radiator got cleaned up too.


Not too bad for the time I had today. Hopefully tomorrow we be productive too. Got to get out to the track! :P

08-16-2017, 10:05 PM
I'm in the prep stages so everything takes forever--lots of cleaning and what not. Some small progress made today.

Cleaned up the rear axle.


Since I was painting a pipe for another bike I sprayed a bit on some of the exposed areas. I really don't have the resources to do this properly this time so just a quick and dirty style.


And this one is super cool. Have yet to try it out, but I filed down a couple of nuts to fit into the space where the bolt goes on the chain adjusters. One of the things about these bikes is the chain adjusters come loose and then the end caps fall out, which then get caught up in the rear sprocket messing up the swing arm. I've seen this on a number of GPRs. They fixed this on the 05 bike with an internal nylock. So I've been wanting to do this on the older bikes for a long long long time. While starting to assemble the rear end of the bike I decided it was time to see if it would work. More photos of it soon, but here's basically how it will work.


08-19-2017, 12:57 AM
Made some good progress today. :)


Checked the rear wheel on the balancer. It was quite good and didn't need any weights.


Here is what the chain adjusters look like with the nylock mod. I still use thread lock too. This may not work out quite so well as when using the nylock the range of the adjuster is limited. I might be able to make adjustments for this with longer bolts.




Installed the rear brake system--looks like I didn't take a photo of the caliper. Have to remedy that next time.


Got the bars on:


Removed the starter:


Put the top chain roller back in. You have to do this before the top shock mount bolt because the chain roller bolt is too long to insert when the shock is in place.



Torqued down the shock and linkage. I printed out the Derbi torque specs from the service manual and keep them in the torque wrench case. It's very nice. :)



Installed the engine, and then set up the torque assembly line. I set all three bolts up with allen drivers.



Torqued down the swing arm axel. You have to loosen this in order to remove the engine because the rear engine mount is part of this assembly, and you it helps a lot to turn it out of the way to remove and install the engine. Make sure to torque this after you torque the engine bolts. Then put the caps on.



And I removed some stickers. I'm still going to have to repaint the faux tank cover, but getting the stickers off is the first step. Also removed some from the frame. There's more on the other body work as well, so Mr. Heat gun wont be too lonely. lolz :P


08-19-2017, 09:45 AM
Another way to go.340236340237A small lock washer will put a little tension on the bolt.

08-20-2017, 03:19 AM
That works if you torque them down after you tighten the axel--which pretty much works most of the time without a lock washer. But it would be nice if the adjusters didn't have to be torqued (and then not retain the adjustment after the wheel has been torqued, because now they will have more pull than they had to adjust the wheel) after an adjustment was made, and that's what I'm trying to achieve. ;)

08-25-2017, 12:50 AM
Another big day for the Track bike. Did a lot of cleaning parts, and started sorting out how things are going to fit. Sometimes fitting is one of the more challenging things with all the various part changes. Also, I learned that the Dixon track wants lots of sliders. I've been doing some thinking on how to deal with them, but I wont be able to get the slider action happening fast enough for the Dixon track day. Which is a shame since I've really been looking forward to it. :(

Still I'm going to keep working hard on this bike to get it ready ;)

It's actually starting to look like a bike!


One of the big things I had to deal with was the forks. I needed to retorque the top bolt. On the throttle side the bolt had come loose. I hadn't used an impact wrench to set these and that was probably a mistake. These were the first GPR fork that I had worked on, and I've learned a bunch since. So not so bad to revisit them, but I did have to borrow a tool, and that made it take a bit longer.


This time I set them at 25mm. I may change this over time. I've found on the track it's nice to have the steering a little bit quicker.


There always seems to be a lot of things to clean!








Controls. These seem to take an abundance of time. lolz Just starting to figure out how things are going to go.




The front caliper in place--not torqued down yet though.


The tank cover I have for this bike is fiberglass. I have a fiberglass tail section for it too, but since I plan on running the stock tank I need to figure out how I'm going to set up access for it. So for now I'm going to run the plastic rear section. All those stickers are going to have to go! lolz


08-25-2017, 12:56 AM
I also took a look at inside the cylinder. Over all it looks okay. Most of the stuff on the walls appears to be reflections from the top of the piston. I intend to run the bike as a stock 50cc for at least a while. I may install a BBK on it, or maybe a performance 50 top end. But for now I just want to put it back on the track. The engine spins, and there is compression, so hopefully it will be okay for at least a little while. ;)











08-25-2017, 09:16 AM
Another big day for the Track bike. Did a lot of cleaning parts, and started sorting out how things are going to fit. Sometimes fitting is one of the more challenging things with all the various part changes. Also, I learned that the Dixon track wants lots of sliders. I've been doing some thinking on how to deal with them, but I wont be able to get the slider action happening fast enough for the Dixon track day. Which is a shame since I've really been looking forward to it. :(

Still I'm going to keep working hard on this bike to get it ready ;)

It's actually starting to look like a bike!


One of the big things I had to deal with was the forks. I needed to retorque the top bolt. On the throttle side the bolt had come loose. I hadn't used an impact wrench to set these and that was probably a mistake. These were the first GPR fork that I had worked on, and I've learned a bunch since. So not so bad to revisit them, but I did have to borrow a tool, and that made it take a bit longer.


This time I set them at 25mm. I may change this over time. I've found on the track it's nice to have the steering a little bit quicker.


There always seems to be a lot of things to clean!








Controls. These seem to take an abundance of time. lolz Just starting to figure out how things are going to go.




The front caliper in place--not torqued down yet though.


The tank cover I have for this bike is fiberglass. I have a fiberglass tail section for it too, but since I plan on running the stock tank I need to figure out how I'm going to set up access for it. So for now I'm going to run the plastic rear section. All those stickers are going to have to go! lolz


Looks like you are doing a fantastic job given the space you have to work in. That pile of tools and parts and cramped quarters would drive me crazy!

08-25-2017, 12:35 PM
To be sure it's a challenge. But that's what I have for now. It would be great to have a shop with a bench and things like a bead blaster, welder, mill, lathe, etc. I know how to use all those things. But I don't so I have to be creative. lolz

08-25-2017, 01:18 PM
Manimal posted this up info from Dixon earlier on another foro:

We want sliders, handle bar covers, foot pegs that fold up.

Due to these requirements I probably wont have my bike ready in time for this Sunday. To get rear sliders I'm probably going to have to take the rear end of the bike apart again so that I can weld on the rear slider mounts.

If you have rear sets on the bike with non-folding pegs they are allowable with sliders on the ends of them. Ed asked them about that since most MiniGP bikes have pegs that don't fold up.


Ed also suggest getting the bar end lever protectors. Woodcraft makes some nice ones (https://www.revzilla.com/motorcycle/woodcraft-lever-guards).


As Denee showed us PitBull makes some weld on bungs for stand spools, and you can get spools that double as sliders. SVRacing (http://www.svracingparts.com/store/#!/Swingarm-Sliders/c/633296/offset=0&sort=normal) makes spool sliders in M6, M8, and M10 sizes. Another option is this the budget way of employing long nuts as illustrated in this photo.



Also there are bolt on solutions like this one from T-rex.


08-25-2017, 01:50 PM
The bikes are so light that I figured I would simply drilled and tap the swingarm. No problems yet. I'm thinking of going back to the Aprilia RS50 but the ones I've looked at are WAY too expensive!

08-25-2017, 02:31 PM
Matt welded on a tube and nut to my GPR swingarm and I'm using spool sliders. I bought off-the-shelf bar ends and replaced the hardware with M5 to fit the GPR threaded hole. My pegs fold up. And I drilled and tapped my front axle ends and mounted the smallest, black skateboard wheels I could find. My mounting solution involved using the standard skateboard bearings on both sides of wheel as if you were mounting it to a skateboard, and using a 10/32" bolt.

Matt's pegs are rigid, and I think he ended up fabricating a Delrin slider with a part that fits into the peg and is mounted with a screw through the bottom of the peg.

08-26-2017, 01:32 AM

The swing arms on these bikes are basically folded sheet metal. Drilling and tapping it wouldn't provide much strength for sliders. You might be able to get away with spools for a little while if you were careful, but I wouldn't trust it. By welding something to the bottom of the swing are you are gaining the strength of two corners, plus creating a bridge. It's a much stronger solution. One that has a much better chance of holding up during a crash.

While some folks may claim otherwise I don't think getting parts for an RS is any easier than getting them for a GPR. Really it's just a matter of knowing where to look. We've already told you that info. And as far as engines go the Derbi has a better transmission. The crank is better too, but if you go performance you'd be changing that on an AM6. You might change it on the Derbi, but you wouldn't have to do it. With the AM6 it becomes important to change the flywheel, which also removes the electric start. I don't personally have an issue with GP starting my bikes, but some people do with their bikes. If that's an important feature it's worth considering--not that the GPR charging system is up to the task of keeping the battery at a state in which it can start the bike. lolz


The bars I have on the track bike are actually Cavigia Mito 50 bars from Domino. The don't have the plug on the end so you can use standard bar ends with them--which is why I put them on the Track bike. ;) I bought some delron(sp?) rod material with which to make bar ends--but it was misplaced in the move. Still looking for them. lolz. But once I find them I'll use the "hand lath" (a hand drill) to make bar ends out of them. :P

I use to have a really nice Miller mig welder. Not as fancy as Matt's welder, but still quite nice. If that was still around I'd be able to weld up a solution. But it was stolen and is no longer an option. Still I think something along those lines is the solution for which I'm looking for the real slider/spools.

For the front--I may have to go with the bolt in the axel, but hopefully I can come up with something better. The skateboard wheels with the bearings is an interesting idea. That way when they hit the turn too. That might keep the bolts from shearing. But if they are set up to turn then you don't get the support from the fork either. hmm

For the pegs I'll either do the hand lath thing, or see if I can get some pegs that have them already. I really wanted to save these rear sets for the Red bike, but that project keeps getting put further back on the shelf. ¯\_(ツ)_/¯

08-26-2017, 10:34 PM
up until last year, all of the parts catalog for the RS was still in production and guaranteed availability by Piaggio / Aprilia. That is why there's no question better parts availability for the RS bikes compared to the older GPR's.

in five years, who knows.

08-27-2017, 09:04 PM
That would make sense if you were talking about this version of the RS:


08-27-2017, 09:11 PM
Having just taken a quick look at available parts on EasyParts it's clearly not true for RSes that were pre-06 bikes. So really they are basically very similar to the Derbi bikes. Which has been my experience for years now.

08-28-2017, 12:37 AM
That's why we squirrel'd away so many spares.

08-28-2017, 12:57 AM
Having just taken a quick look at available parts on EasyParts it's clearly not true for RSes that were pre-06 bikes. So really they are basically very similar to the Derbi bikes. Which has been my experience for years now.

Aprilia had to offer a complete list of spares and parts for at least 10 years after the models are sold in the usa. the last 2005 RS50's were sold in 2006. after july of 2016 a few of us big spenders with AF1 were old that if there's a rare part or something needed brand new from aprilia to order it now because after november it would no longer be guaranteed availability. that is, they would no longer have to run a production for even a single order, as they did previously. like when my dad and i ordered chain guards and there were none in italy and none in america. you are welcome because in 2014 my dad and i ordered six of them and piaggio did another production run of like 100 or whatever it was. so yes, in 2016 you could still purchase any part in the aprilia catalog for the 2005 RS50, which fits the bike back to 2000. you could even get brand new marzocchi fork tubes, fairings, you name it.

now that they no longer have to provide you spares availability, as they run through what they have in inventory, they may choose to no longer restock certain items. i don't know what easy parts pays you, but you are clearly wrong on some of this

08-28-2017, 10:20 AM
Matt the ten year thing is true for all motor vehicles sold in the States, which would apply to Derbi as well. And for quite a long time now Aprilia and Derbi have been under the same parent company. You can even order GPR parts from AF1. Some of them are even in their warehouse!

Easy doesn't pay me anything. You can just as easily go on their website and see what parts have been discontinued. All I'm saying is that for both bikes the parts availability is about the same. Sure because AF1 is in the States it's very convenient, but with shops like EasyParts, MaxiScoot, Planet, etc. it's actually not all that difficult to get things for the Derbi. Treats even stocks stuff for them too.

08-30-2017, 12:02 AM
Like most of the days recently it was a Track bike day. lolz

First I went to Treats. For a moment I thought this would be all I needed to finish building the bike (for now). I was of course incorrect--which I would discover very quickly.


Much of the day was spent rooting around for parts like this spacer that is part of the upper radiator mount.


I didn't find all of the things I was searching for, but I did find some fun stuff--like this brand new plug.


After hours of searching around I did some more engine cleaning. Once I too the stator cover off I found a lot to clean. It's cleaning up nicely though.


Then I started fitting the carb. The sad part is that all of the intakes I have are for the 24mm carbs. So I'm going to have to visit Treats again! lolz


Here's the swap out of the float bowl for one with the main jet access port. This is a nice feature on a street bike, but a really important one on a track bike where it's necessary to re-jet for the track/day's conditions.


The carb with the air filter. The idea here is being a track bike I'm probably going to have to tune for the day/location anyway so some of the advantaged of the air box wont be enjoyable. Still one advantage of the air box is that in provides "clean" air. Now I don't mean air with particles in it, I mean well let me have this guy explain it...


For the carb you want air with less turbulence. I'm hoping that by getting a big filter up inside the faux tank there will be cleaner air then down by the wheel. The best thing to do would be to make a box like the GP bikes have--if I was Scotty I'd make a carbon fiber air box to sit in there.

I ended up getting this huge Polini filter with the 90° coupler. This sticks the filter way up into the engine compartment. The one major disadvantage of this setup is all the hot air from the radiator is going to go directly into the air filter, and that kind of sucks. Engines like cool condensed air, not hot expanded air.






I also installed the OMG high flow 8mm petcock.


08-30-2017, 04:59 AM
compressed air not condensed... wet air generally makes less power than dry air

09-02-2017, 12:23 AM
compressed air not condensed... wet air generally makes less power than dry air



09-02-2017, 01:18 AM
Today in San Francisco was a scorcher. I heard 107°F (~42°C)! Yeah I know some of you cats say that's nothing, and well for you sure, but remember normal temps here are like 65°F (~18°C). So for me it was roasting! Still I was rather productive on the Track bike today. Mostly a bunch of little things getting sorted out, and it all adds up.


First I went to Treats to get the proper intake, some fuel line, and the red fuel filter. These are really cool. They open up, are cleanable, and Treats even sells a replacement core!


Now for a bunch of intake photos. I was going to put a Top intake on this bike, but I only had the PWK size versions. I thought I had the CP/PHBG size, but I didn't. I did have an unopened Malossi PWK kit, and Benji let me swap it. Still since I'd never actually put the Top on a Derbi engine I thought I'd check it out, and compare it to the Malossi. I like the Top intake a lot--it's black! Still I went with the Malossi for this bike--you'll see the Top fitted to another bike soon. I think the notch in the plate is there for the AM6 which uses a bracket for the clutch cable.

Also, comparing the stock reed block fitted with carbon fiber reeds. I did use the Malossi reeds though.








Then I had to check the fitting of the carb. It came out well enough, but I can see why some folks have been having a challenge with this--if you don't fit the carb into the intake before you install the intake you don't have the leverage to get the carb fitted all the way in. After you've done this a few times off the bike the rubber loosens up a bit, and then you can do it on the bike. The manifold should go all the way to the stop on the carb.

Another trick is to get the drain spigot to sit in the little trough next to the engine serial number plate and the kick starter knob. This allows it to fit fairly well. The float bowl is still at a bit of an angle. There are a number of companies that make a spacer plate to fit in here, but then you are moving the carb back, and that effects the quickness of your throttle response.

Another nice thing about the CP is that it has a vacuum connector right at the intake side of the carb. This is a very nice place to add a resonator. Something I may attach in the future.

I started messing with the cables to the carb. It looks like the choke cable I had planed to use is too long. The throttle cable should be fine, and I have a number of throttle tubes with different rates that I should be able to sort through for the right amount of turn. That's for another day though.







I had to add oil to the throttle side fork. For these forks they take 175ml of 10 weight fork oil. The GPRs have a number of different forks, so those numbers are only good for the older forks. These forks are from a 2000 GPR with 16" wheels. The 2004 forks use 140 ml of 10 weight.





I also painted a couple of parts. The radiator lower support, and the shift lever.






Siliconed the seat support rubber.


Well that's all the images I can put in one post. I'll have to put the rest in the next post!

09-02-2017, 01:33 AM
With the fork oil added I could now mount the front wheel. It's only in place because I still need to make a bracket for the speed sensor of the MyChron 3 which will eventually make it to this bike. I also still need to balance this wheel, so it will come off for that, but I just wanted to check that everything was going in the right direction.



On the previous Track bike I ran the HPI internal rotor ignition. I'm going to run that same ignition on this bike. Today I started fitting it. First I had to remove the stock Ducati ignition. It was very clean. I can tell that the cases on this engine have never been split, because this ignition had never been removed.

You have to take the stator off before you can remove the mounting plate. The plate is thread locked, and the little screws can be a bugger to remove. I had to employ an impact driver!





This HPI is actually for a Puch. The taper is the same so it work on the Derbi, but I did have to mod the mounting plate, and it's a struggle to get it centered. I've only got it partially in place, and will deal with that when I set the timing. Because the mounting plate doesn't really line up with the Derbi stator mounts only two of the mounting bolts can be use.



Secured the front tank mount with shiny stainless socket head bolts.


Worked on the radiator over flow tank a bit. I got the top line connected. The bottom line I have to replace. This appears to be a tank from a Senda that was fitted to the bike. The did this because the had employed a different fuel tank. I actually prefer the tank under the seat. There are those that say it ruins the handling of the bike. I disagree. It's lower when located under the seat, and most of the time you don't have to fill the tank up to full on the track anyway. This leaves the engine compartment very easy to access. A big win in my book.

Anyway, since they did this the bolt that secures the over flow tank doesn't really support it. The stock over flow tank has a support system built into the fuel tank. I'm going to have to come up with some additional support for this tank. I'm probably going to silicone some rubber on the bottom of the tank so that it can rest on the subframe.


And that was a full day of wrenching on the Track bike.


09-02-2017, 07:26 AM
are you going to run your carburetor vent / overflow hoses to a catch can? That's required at our tracks in fl

09-02-2017, 11:01 AM
Yeah that's the eventual plan, but I'm still pretty far from that yet. I have the catch can, but I need to get the hosing, and also decide where to mount things. It's kind of amazing how many things I have yet to do on this bike! lolz

Still I'm really pleased with how the bike is coming along. I learned a lot on the previous Track bike build, and having these two used track bikes was interesting because I got to see how two other folks thought about solutions to track prep a GPR.

09-02-2017, 01:34 PM
have you ever tried the vforce reeds on a gpr

09-02-2017, 05:42 PM
I haven't, but will probably try it at some point. The Malossi reeds come with the intake and that was the nicest intake at Treats so I started buying them. It would really be nice to have a dyno and do back to back tests with the various reeds available for these bikes.

09-09-2017, 02:36 AM
Ed blasted the pipe for this bike, and it looks a lot better. I also picked up some hose for the radiator from the auto parts store.



Today I sprayed the pipe. Hopefully it will be dry tomorrow!


Cut and put the hose in place. Need some clamps now.



Cable play went both ways today. Some of it got worked out, but a lot of it didn't happen. The carb turns out to have a stuck choke plunger. These bikes are a bitch to start without the choke, but it should be warm at Atwater so hopefully it will be okay. The clutch cable was interesting. I had ordered a new after market clutch cable. The stock cable has a nylon cover that can be removed. The replacement doesn't. For the aftermarket lever that I have the aftermarket cable wont fit! So I'm going to run an old cable for now.



The sprocket cleaned up clearly needs to be replaced so I'm going to order a new one. Until then this will be okay.



I thought I ordered a 136 link chain, but I must have clicked on the 132 link, because that's what showed up.




The throttle system is really important. I like a nice crisp throttle, and if it's not it has to be worked on. I had all kinds of issues getting this happy, but a can of WD, and a bit of rotary tool work, and I had it working nicely.


09-19-2017, 08:12 PM
No photos for today! Friday I was able to swap out the carb. The first one I got had a stuck piston in the choke cylinder. Benji swapped it out for me and I was able to connect the choke lever, and throttle such that it's working nicely. I also picked up a second chain to get 4 extra links! lolz. Oh well. ¯\_(ツ)_/¯

Hope to make some progress later in the week on this bike.

09-27-2017, 12:21 AM
With all the riding, and having to prep the street bikes I've not been able to get to the track bike. Today I made a little progress. Most of the day was sanding the faux tank. It had some pretty deep scratches and chips in it. Eventually I got it good enough. Did a quick temp coat of Red to get through the weekend. Eventually I'll be getting to all of the plastics, but this is just for now.

I then finally got to the leak down test. Picked up some more bubbles. ;) It looks like things are okay. I had a hard time sealing the exhaust port because the rubber freeze plugs were too large for the 50cc cylinder exhaust port.

Once the leak test was accomplished I finished the carb install. Then moved on to the exhaust. The center mounting point is really far off, so I'm going to have to fashion a bracket. For now I've rigged up a rear support with some strapping. It's not idea, but it will function for the weekend. ;)

And that's all I was able to get to today.















09-27-2017, 01:40 AM
Well I may have found a slider solution (https://tstindustries.com/Womet-Tech-Universal-Mini-Bike-Axle-Slider-Kit.html) for the axels--well for three sides anyway. ;)





09-27-2017, 04:04 AM
Absolutely love this thread!

09-27-2017, 09:48 AM
Well I may have found a slider solution (https://tstindustries.com/Womet-Tech-Universal-Mini-Bike-Axle-Slider-Kit.html) for the axels--well for three sides anyway. ;)

It's that fourth side that's the bear!

09-27-2017, 02:45 PM
It's that fourth side that's the bear!

Well the Grom uses a tiny 19mm nut. The GPRs employ a 22mm nut. Thus it's likely that these wont work, because you've still got to be able to fit a socket into the slider cup. It's a little bit surprising that the Groms use such tiny axels, but then again Honda--they suck.

09-27-2017, 06:49 PM
Well the Grom uses a tiny 19mm nut. The GPRs employ a 22mm nut. Thus it's likely that these wont work, because you've still got to be able to fit a socket into the slider cup. It's a little bit surprising that the Groms use such tiny axels, but then again Honda--they suck.

I recall that you posted a picture of, I think, a later model GPR that had axle sliders that fit over the existing nut and used a locking pin that goes through the slider, nut, and axle. I like that setup, but of course my vintage doesn't have that (but I could retrofit), but that still wouldn't work for the front right side of our axles, since it's flush with the outside of fork. I'm fairly happy with my drill and tap and skateboard wheels on the front axle. It doesn't look too bad, though I don't know whether the bolt would snap off if I wrecked. And the rear I just did spool sliders, which are useful anyway.

09-27-2017, 11:53 PM
Absolutely love this thread!

Thanks--there's lots more to come. ;)

I recall that you posted a picture of, I think, a later model GPR that had axle sliders that fit over the existing nut and used a locking pin that goes through the slider, nut, and axle. I like that setup, but of course my vintage doesn't have that (but I could retrofit), but that still wouldn't work for the front right side of our axles, since it's flush with the outside of fork. I'm fairly happy with my drill and tap and skateboard wheels on the front axle. It doesn't look too bad, though I don't know whether the bolt would snap off if I wrecked. And the rear I just did spool sliders, which are useful anyway.

Yeah that was for the 2010-2012 models. I'm probably going to weld some stuff on to the swing arm eventually.

09-28-2017, 12:10 AM
Little steps is all I seem to be making these days. I went to the Daly City Tool Mart to pickup a tap, and drill bits for the slider action. Then I went to Tap plastics and picked up some Delrin rod.

Using the hand lathe I started working on the bar ends. Because my center hole wasn't center enough the progress is really slow.

I also put in some time sanding the tail section. The fucking sticker are a pain in the ass. Even with LOTS of acetone getting the sticker gum off of the tail section has been a nightmare. Will have to work on it some more tomorrow.

Then I did a bunch of little things. One of which was replacing the philips screws holding on the oil pump replacement plate. Not only are they ugly, but they were stripped too. Had to employ the impact driver to remove them. The have been replaced with shinny new stainless socket bolts. ;)

I also put some support in for the water over flow tank. Just a piece of hose siliconed to the tank and frame. If it's not enough I'll come up with another idea.

Installed the well-nuts for the tail section, and added some hose clamps to the water over flow tank. And that's about all I had time for today.


















09-28-2017, 05:52 AM
I had a similar tail section on my first RS50. I was using it for the street so I cut a hole in the top, painted it and made my own "pillion pad" so I had a storage spot.343011

09-29-2017, 11:25 PM
More little progress today--and the ants came back!

I thought I took more photos, but apparently I didn't! Most of the time was spent sanding. It takes forever to sand. The painting didn't go all that well, but it's fine for now. The ants showed up climbing all over one of the tail section halves.

Finally removed the pins that hold the controls. These where in the way of the controls I wanted to employ. So I removed them with the rotary tool, then shot a bit of paint on them.

The clutch lever I had came with one of the source bikes. It looked nice enough, but I needed to drill it out to fit the cable. This was a bit more difficult than I expected, but eventually I got it working. The clutch level is okay. It could be the cable, but it feels a bit tight.

I went to take out the thermostat. It was really grunged up, and stuck inside the head. Eventually I was able to remove it one piece at a time. But now all of the coolant lines are connected.

I was also able to get the chain in place. Turns out I didn't need any additional links. Which was nice. ;)














10-01-2017, 12:53 AM
Got a lot done today, but not enough to go to there track tomorrow. ¯\_(ツ)_/¯

I ran into a number of gotchas. Kind of what happen with used bikes.

Started today with checking out how the tail section was going to look.


Then set in on repairing the cracks. I didn't have the stuff around to do this before the paint, or I would have done this first! lolz It's good to have some source materials. I was out on a group ride some many years ago and this idiot crashed his 748 into a bunch of other riders. I picked some one of the fairing pieces knowing that it would come in handy. I've used this on a number of bikes! lolz





There were lots of little things to clean and paint too.








Then it was time to drain the tranny oil. To make this jorb easier take an oil bottle, cut a tongue, and use it to keep things from spilling. This works great because these trannys only take about 650ml.




This was working great until I open up the drain plug at the clutch cover. Then a huge amount of fluid came out! I had planned on revisioning the water pump because these things go out, and one of the bolts holding the pump cover on was quite oxidized. Clearly something had failed, and the clutch cover was full of nasty shit. Took a really long time to clean out. The clutch plates were all stuck together too. Eventually it was serviceable again, but by that time I was far too late in the day to expect the bike would be ready for tomorrow.







Trying to figure out how to fit a kill switch into the mix.


Tail Section Assembly



10-01-2017, 12:56 AM
And a few more photos push to another post due to the 25 image per post limit on AF.

The bike is coming along. ;)




10-05-2017, 10:33 PM
Made some tiny progress today. I made some progress on the water pump as well, but didn't take photos of it yet. Still lots to do! lolz

Finally made it over to Treats to pick up the clutch springs. They are stiffer than stock, but look almost the same. The coils are same, and the springs are the same high, but the thickness of the wire is slightly larger.




Picked up this gasket remover--it didn't work very well at all.


Finally installed the fuel line and filter.



10-07-2017, 02:57 AM
Made a lot of progress today. Even got the bike started! It runs great. It's going to be a lot of fun. But I wasn't able to finish enough of it to go to the track tomorrow. I needed to finish some brackets for the body work. I was out of time and had to call it quits for the day--still it was a great day of wrenching, because I got to ride it.


First up was was getting the water pump assembled. The revision kit had a shaft that was too large. This gotcha was pretty bad because I wouldn't be able to use this kit. I ended up using the old shaft with the new seals.






So with that worked out I went at the timing. This was rather difficult, and I even bent my new tool! But I kept at it, and eventually I was able to modify things enough to finally get it set.





Once that was taken care of I was able to button up the clutch cover.


Then I was able to tighten up the pipe again.


The next issue was the 23mm CP carb. The slide was sticking. I've never run into this previously. It took me quite a while to figure it out too. What was happening is the stop where the idle screw contacts the slide. The slide was deforming and then causing it to stick when the throttle was pulled. I was finally able to get the carb to work correctly with some rotary tool and 1200 grit sand paper action. Not happy about needing to do this sort of thing on a brand new carb. I didn't get any photos though, as I was trying to meet my deadline.

Then I went around torquing bolts, and nuts. I also added oil to the tranny, coolant to the cooling system, mixed up some fuel and poured it in the tank, oiled up the filter, and, added a kill switch. A lot of little things had to be done.




Then it was time for a test ride. Oh boy oh boy oh boy! Lots of fun. I first rode it in the parking lot with out any gear, and it was obviously too fast, so I put some gear on. Then ran it up and down the lot more than I probably should. It doesn't feel like a 50cc. It's got a lot more drive. It even wants to lift the front. This is probably due to the 12 tooth front sprocket. The clutch lever is garbage and I'll need to replace it with something better. The brakes work, but they need to be a lot better. So I'll have to attend to them. I have some Ferodo pads which will probably get put in there, and the fluid really needs to be changed out.



Okay after the fun I still had a bunch of work to do as the body work need to be fitted. I was only going for the tail section and the faux tank, but because I needed to make brackets I wasn't able to get done before I had to pumpkin. One of the previous owners did some interesting stuff with cutting up the stock tank and fitting in a tank from another bike--probably a Derbi Senda. He also had some velcro to hold things in place. I decided that I would use some of these parts, and see if I could make it slightly better. I've not finished yet so photos will be in a later post.

This is taking a lot more effort than I had initially expected, but I'm very happy with the progress, and how much fun the bike is to ride. I'm really looking forward to taking it to the track even if it wont be tomorrow (Saturday). ¯\_(ツ)_/¯





10-11-2017, 11:16 PM
The faux tank and tail section are installed. This means that stage one is complete. I can now take this bike to the track! Obviously it's going to get updates, and more features as I have time to implement, but there's now enough there that I can start riding it.


For the faux tank mount I needed to make some mods. But I didn't really take many photos this time either. So I don't have any photos of the brackets. But in the future I'll be painting them so all in due time. I will say this, the faux tank is the most stable I've ever felt on this style GPR.




To gain access to the fuel tank I need to cut a hole. I decided to try a flap. This seems to be working. Eventually I'll install the fiberglass tail section, but until then I'll be running this stock plastic section.




Are you ready boots? I did ride it some more in the parking lot today. This is going to be so much fun!



10-14-2017, 10:16 AM
Are you ready boots?

now that is some 2005 motogp shit i haven't heard in a while

10-15-2017, 01:04 AM
now that is some 2005 motogp shit i haven't heard in a while

lolz--was it really that long ago? Seems like yesterday. ;)

10-25-2017, 12:58 AM

Track Day

This Sunday October 29th we’ll be taking it to the kart track at Stockton Little 99 (http://www.stockton99.com/little99_info.html). Join us for some full throttle action on the track. Expect it to be warm so bring shade, beverages, snacks/lunch, and other supplies.

Prep the track bikes, get the chains lubed up, the tires checked, and get that riding gear ready. Smaller (50~85cc) two stroke replicas like the Derbi GPR, and the Aprilia RS50 are very much encouraged. Fast mopeds, pocket bikes, Groms and such are okay!

Meet up Sunday October 29th
The track is open from 10am to 5pm. Open track, ride all day for $40.

10-28-2017, 02:02 PM
This was for another thread (http://www.apriliaforum.com/forums/showthread.php?275584-Derbi-The-Red-Power&p=4343034&viewfull=1#post4343034)--and is there now. ;)

10-28-2017, 02:52 PM
Are you ready boots?



10-29-2017, 11:08 PM
We had a good time out at Stockton today. For the most part things went really well. The bike were running good, although Mike's need some serious mid throttle tuning, and mine had a clutch cable fail. It started to bind up--which is unfortunate since it was a brand new cable. I'll be checking into it, and will probably put an older OEM unit on the bike.

There were a lot of people out there today. I didn't get much in the way of photos because I was rather busy doing riding. I was surprised how many LARGE cc bikes (over a liter) were out there. That track is just way too small for those bikes--and it's not safe having them out there with the pocket bikes.

Ed picked up Max's MetraKit for Alex today. It needs some fixing up, but I'm excited to see what Alex can do now that he'll be on a two stroke again.

Photos from today at the track!















12-09-2017, 10:29 PM
PhotoBucket has decided to extort their customers. I've switch to using Imgur for the new stuff. You can view the older posts in this thread in two ways.

First you can use the Chrome browser with PhotoBucket fix extension (https://chrome.google.com/webstore/detail/photobucket-hotlink-fix/kegnjbncdcliihbemealioapbifiaedg).

Second you can view it with most any browser over at GPR Camp on the foro (http://gprcamp.com/foro) there. I've split it up into a number of threads.

Derbi GPR Track Bike (http://gprcamp.com/foro/viewtopic.php?f=15&t=37&sid=c8d982b1c1ca27d3b3795bf732c79d1e)

MT Mike's Track Bike (http://gprcamp.com/foro/viewtopic.php?f=15&t=71&sid=c8d982b1c1ca27d3b3795bf732c79d1e)

Cobra CX65 Mini Moto (http://gprcamp.com/foro/viewtopic.php?f=15&t=78&sid=c8d982b1c1ca27d3b3795bf732c79d1e)

PPMPR: Project Poor Man's Pro Race (http://gprcamp.com/foro/viewtopic.php?f=15&t=49&sid=c8d982b1c1ca27d3b3795bf732c79d1e)

Please do check out these threads. There's lots of great information within!


02-09-2018, 09:41 PM
Picked up something really nice at Treats today for the track bike.




03-31-2018, 02:57 PM

We finally did the PWK carb upgrade on MT MIke's GPR. This included the Malossi intake reed kit as well. For the carb we went with the Polini 24mm PWK. Mike had a K&N filter that we used, as the Uni filter on the TM24 doesn't fit the PWK.

The main jet that came with the carb was a 105, which seems to be working great. We'll probably have to do some tuning at the track, but for now the bike is running very strong. Better than it has since we picked it up. Should be a lot of fun on Thursday.



05-30-2018, 09:27 AM

It got up to 90°F out there!! Yes it was a hot day, but thankfully there was a constant nice breeze that helped to ameliorate the higher temperatures.

A good number of folks made it out. This was also the first time for pocket bikes at Sonoma, and it worked out great. The track gave the minis our own session so we did't have to ride with the motards. This made the day infinitely better.

Daren came out with his 65, and was educating all of us with technique—as you can see from the photos he was ripping around the track. Ben and his buddies on the pocket bikes were also smoking the corners. There were some other folks out there an Groms and such too. Very fun day at Sonoma.

























05-30-2018, 09:28 AM








06-01-2018, 10:16 AM
Awesome pics. Looks like a fun time was had by all.

06-01-2018, 10:24 AM
Yeah we are having a blast out there this year. Finally everyone has a working bike, the weather has been great, and there's been lots of track opportunities.

06-01-2018, 01:36 PM

Ride Report

This was an awesome day at the track. Joe, Rob, Mike and I headed out there with our minis. Daren was there with his 65, Max showed up with his 65, Kimi was there with her friend both on 65s, and there were even a couple of Groms out there too.

I have to say it was a total joy to be on the track with these awesome riders. It was like having a private lesson. Each time they would pass you they'd show you how to take the corner, and if you didn't catch it you'd just wait until the next lap where they would show you again. It was so cool.



















06-01-2018, 02:05 PM
Kinda sux being the photog, no pics of yourself on the track :)

12-14-2018, 04:41 PM

Saturday March 31st was Dyno Day at Nor*Cal Cycles. They not only ran free runs on the dyno they provided a yummy lunch. I shot some video so hopefully I can make a decent edit out of it. My bike had trouble on the Dyno. Not really sure why though. The bike was couldn't pull the dyno all the way into full throttle. I did get one run in third gear that did okay, but that was about it. Still wasn't opened up all the way though.

Edit: Upon investigation it was the HPI. :eek:



01-03-2019, 04:00 AM
Alex made it into Motorcycle.com (https://www.motorcycle.com/manufacturer/benelli/24-hours-of-silliness-aboard-the-benelli-tnt135.html)!!!


01-05-2019, 07:25 PM
look at his focus, go kid go :peace:

01-06-2019, 04:21 AM
look at his focus, go kid go :peace:

Alex is a great kid. Super cool to see him getting national recognition. :cool:

02-03-2019, 06:48 PM

Track Day

This Monday February 18th we’ll be taking it to the kart track at Sonoma Kart Track (https://simracewaydrivingschool.com/programs-experiences/go-karting/). Join us for some full throttle action on the track. Expect it to be warm so bring shade, beverages, snacks/lunch, and other supplies.

Prep the track bikes, get the chains lubed up, the tires checked, and get that riding gear ready. Smaller (50~85cc) two stroke replicas like the Derbi GPR, and the Aprilia RS50 are very much encouraged. 65s, pocket bikes, even Groms and Zs too!

Meet up Monday February 18th
The track is open from 10am to 5pm. Open track, ride $25-40.

Sonoma Kart Track Location (https://goo.gl/maps/29e6SvFRMVs).

02-04-2019, 04:39 PM
Can't wait to see pics/videos of this event!:D

02-04-2019, 07:57 PM
Can't wait to see pics/videos of this event! :D

If you follow this link (http://gprcamp.com/foro/viewtopic.php?f=8&t=367&sid=ca8a2c9886c84cc2396b570b9a1c5a63) you can find photos from previous track days, and if you check out that section of the foro there are a bunch of previous track day events.

02-18-2019, 12:18 PM

It was time to prep the track bike for the Monday event. I hadn’t been able to get the bike running recently, and I suspect the cold has had a lot to do with it, but I also found that the throttle adjuster had been wound way out. This would also make the bike hard to start since the carb would be open keeping a rich mixture from occurring to help get the engine going.



With the engine sussed out, and the bike running well again I did a quick check on the tire pressure. The bike should be ready to go tomorrow. It will be fun to ride it again, as it’s been far too long. :paw_prints:


03-09-2019, 03:20 PM

While waiting for Mike today I got a hand full of photos.






03-26-2019, 01:07 AM

A significant amount of time has gone by since we’ve been out to Sonoma for some mini moto kart track action. Most of this year we’ve been looking forward to a day which might be pleasant enough to allow some two wheel fun. With the rains nearly every opportunity had been washed out. However, it looked like President’s day just might be dry enough—with bated breath we waited, and our patients was rewarded.

Before you can ride the track you have to get there first. Thankfully the drive out to Sonoma is filled with wonderful vistas. I didn’t get some of the more famous shots, but here are some nice green ones for which to feast your eyes.





When we got there it was cold! But it's always a lot of fun to get back to the track so we weren’t really put off. Earlier in the day we had a bit of a slow start, and some folks had things come up that precluded their participation which was sad. However, when we arrived we were treated to a pleasant surprise of a number of 65s! The scene is still hanging in there!





Shortly after we arrived RD and the gang showed up with their three strokers which they quickly unloaded, and proceeded to prep for some circuit activity. GX, Joe, and RD were hot on it, and ready for the track much faster than we were prepped.





The track was laid out in national mode today, which means the long straight running in a clockwise configuration. Mike and I got our bikes out of the truck, warmed them up, got ourselves suited up, and went out for some riding. The surface was a little bit slippery, but not too bad for the first two sessions. The third session though was sketchy as the sun had started to duck behind the hill at the back of the west side of the track.





The time soared by and before we knew it the fun was over, and it was time to pack it in. It’s all good though. We had a a good time, got to shake out the cobwebs, meet some new friends, and enjoy another wonderful day at the track. :paw_prints:





04-01-2019, 05:53 PM
Note: this project started back in February of 2017!!! So these are some old posts until I get caught up.

I've been talking about these bikes for quite a while—an American made two stroke (http://cobramoto.com)! Yes you can actually buy a brand new two stroke motorcycle made in the States. Currently they only make dirt bikes, but I really hope they start making circuit bikes, and this is one of my motivations for getting a Cobra over the other options. One of the trends at the track is to take a 65cc dirt bike and set them up for Mini Moto. Most folks get a KX65, but some do get the 65SX. Both are nice bikes. The KX is generally less money, and the KTM is more, but I didn't want to go with either one since there was an even better option!

The Cobra CX65
Cobra started in 1993 and are based in Michigan. They are focused mainly on race ready PeeWee moto crossers. They basically build a works bike that can run in the stock class. Because they already come with all the bling they have a huge advantage over the Japanese and Euro bikes. For those bikes if you set them up with the same gear they wouldn't be stock, and thus would have to race in a different class. For this reason Cobra just totally dominates the PeeWee classes from entry level 50cc to 65cc.

These bikes are truly amazing with custom parts everywhere. Even the frame is made of custom high carbon steal rolled into oval tubes specifically for Cobra. The cases look like they are billet. The bike is incredibly fast—and I may have to detune it for the KSB drills (http://ksbsport.es) that I want to run. Still it is an awesome bike that's way better than the competition—and yes Virgina it has a power valve. ;)

The one I picked up is a 2013 model. It raced for about three seasons, and won quite a few races. :) I'll need to do a bunch of set up on it, and replace a few parts here and there. I also intend to get some sliders, and change out the wheels. I may lace up some proper sized rims to the stock hubs, or I may just get some mags for it. I'd like to get the mags because then I don't have to deal with tubes. lolz The Mini Moto guys have worked out most of the mods for the other brands so it's just a matter of adapting the knowledge.

The Micky Dee's color combo is a bit off putting, but they do sell the plastics in all black, or all white, and I'm quite grateful for that option. lolz Yes, I will take fries with that...







04-05-2019, 02:21 PM
Some bits showed up today. :P


Is this for GPR camp ?

These parts are for the Cobra, which I'm setting up for doing drills, but will also have a mode (by doing a carb change) to take out on the kart track. It's a really fast bike, so I need to restrict it for doing drills. But on the track having moarrr powaaa is well, fun. ;)

I'm probably going to bring the Cobra to the camp site though since there's a huge parking lot, and a long private driveway. I'm really looking forward to having some fun there.

I do have, and will be ordering more bits for the GPRs. I think lots of folks are doing EasyParts, and MaxiScoot orders. Another good one is Scoot Fast (https://www.scootfast.net) (like in the previous post). They have a bunch of neat bits I've not seen on the other sites.

Oh and Easy just did a facelift on their site!

04-06-2019, 04:18 PM
Please note: I cannot support K and J Racing as Kevin, the owner, is not a responsible man. He sent me damaged goods, and pretended that he would do something about it, but never made good on his promises. He always blamed his suppliers for which he claimed to be in business with, which it turns out according to them they are not. This means that if you buy sometime from Kevin then it is not considered a new product, but rather used goods with no warranty. This is a deceitful practice. I am personally out hundreds of dollars, and a lot of time trying to deal with Kevin.




04-07-2019, 11:04 PM
After some cleaning the hub was ready to lace up. The directions for lacing the wheels were pretty interest, and figured some of you might like to read them. The bummer came when I started to true them up, and discovered that the spoke wrench doesn't fit the new nipples. ¯\_(ツ)_/¯ Gotta get another wrench. :/

Still it's going to be sexy when it all comes together. :)