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View Full Version : My RS50/KX125 hybrid



Crim
10-27-2010, 07:42 PM
So figured I'd post up some pictures of what I've been working on. Back in April or May I picked up this rolling RS50 chassis from a forum member.

http://sphotos.ak.fbcdn.net/hphotos-ak-snc3/hs472.snc3/25892_704577888327_22613477_38779902_1108712_n.jpg

http://sphotos.ak.fbcdn.net/hphotos-ak-snc3/hs491.snc3/26833_704668970797_22613477_38782804_582211_n.jpg

A couple months later of trolling craigslist I picked up a sweet running 1994 KX125 for cheap. I took the KX125 out to play in the dirt and I was hooked! It wasn't until a couple weeks ago that I could manage to tear apart the KX. That bike is just so much fun to go trail riding on.

Anyhow, I more or less followed this guy on how he built his engine subframe: http://www.rhotation.com/bikes/rs85/rs85.asp

Starting the subframe:
http://sphotos.ak.fbcdn.net/hphotos-ak-snc4/hs265.snc4/39582_754806210367_22613477_40268522_1154186_n.jpg

http://sphotos.ak.fbcdn.net/hphotos-ak-snc4/hs989.snc4/76226_765771830177_22613477_40491822_1808237_n.jpg

Engine hanging from mock motor mounts so I could properly align everything:
http://sphotos.ak.fbcdn.net/hphotos-ak-ash2/hs442.ash2/71590_755369666197_22613477_40284808_2546625_n.jpg

Engine cradle mostly finished, I need to trim off the extra bits and coat/paint it still:
http://sphotos.ak.fbcdn.net/hphotos-ak-snc4/hs902.snc4/71547_762130612207_22613477_40409999_565404_n.jpg

And with the fairings back on. The engine fits like a glove, and I even managed to be able to keep the kick starter. I think I mounted my engine a bit further forward then most of the other guys I've seen do KX swaps on here.
http://sphotos.ak.fbcdn.net/hphotos-ak-ash2/hs004.ash2/33586_762150746857_22613477_40410340_7910998_n.jpg

So whats left? I need to mount the radiators, and I need to make an exhaust fit. Following Cafe750's lead, I've got an RS125 exhaust coming, and hopefully I can modify it the same way he did w/o much trouble.


-- Update Nov 4th 2010

Mostly finished her up. fitted the modified RS125 pipe. I temporarily/half-assed welded on the stock KX125 silencer to keep my neighbors happy, but I have a nice carbon fiber can on its way.

The radiator lines are less than sexy, and I may end up having issues with trapped air, I believe the radiator fill cap needs to be the highest point yeah?

I just rode her up and down my driveway a bit, seem as tho I'm getting coolant into my oil Guess I need a new water pump shaft and seal. Weak!

http://sphotos.ak.fbcdn.net/hphotos-ak-snc4/hs928.snc4/74108_765772249337_22613477_40491832_4487707_n.jpg

http://sphotos.ak.fbcdn.net/hphotos-ak-snc4/hs1146.snc4/148889_765772189457_22613477_40491831_8358547_n.jp g

http://sphotos.ak.fbcdn.net/hphotos-ak-snc4/hs889.snc4/72219_765772289257_22613477_40491833_6103394_n.jpg

http://sphotos.ak.fbcdn.net/hphotos-ak-snc4/hs975.snc4/76814_765772364107_22613477_40491835_1361684_n.jpg

-- Update Nov 11th 2010

Fitted a proper carbon silencer from TygaRacing onto the expansion pipe. I think I did a pretty good job lining the can up at the proper angle and position.

http://sphotos.ak.fbcdn.net/hphotos-ak-snc4/hs960.snc4/75359_768676594007_22613477_40538748_2851040_n.jpg

I also ordered a stage6 remote choke cable and adapter for my carb, but the adapter came missing a piece....arrr. I think the remote choke is pretty trick looking tho. Whenever I get around to making a new dash I'll either flush mount it into the dash, or maybe mount under the tank opposite of the fuel petcock.

http://www.scootercraft.com/media/catalog/product/cache/1/image/320x240/613cb59592aba8beba9d77b5f9846961/e/t/et-s63199900.jpg

-- Updated Dec 11 2010

And finished (sort of). Next up is ordering a lighting stator so I can get all the lights working, but I'll probably wait closer til Spring to do that, its gotten too cold to have fun outside here in the past couple of weeks. I did take it out around my neighborhood, took awhile to get warmed up, but I can tell its definitely going to be a fun little bike. 1st and 2nd gear seem to spin by too quick to really get a feel for the power...With no tach I'm assuming I'm hitting the rev limiter because as soon as it feels like its starting to get moving it falls on its face. Once I get it up into 3rd however you can feel it take off. I was extremely skeptical, but this RS125 expansion pipe definitely does its job! :D

http://sphotos.ak.fbcdn.net/hphotos-ak-snc4/hs1216.snc4/156874_780143354527_22613477_40738906_6863677_n.jp g

Crappy cellphone video of it idling:
http://www.youtube.com/watch?v=qEN3JIRSY8A

Created a thread about the LED headlight setup I made for it: http://www.apriliaforum.com/forums/showthread.php?p=2737968

xXxKillDogxXx
10-27-2010, 07:56 PM
im really liking this keep us posted would love to see this finished :D

SuperhawkLGT
10-27-2010, 07:57 PM
Sick!

bikebike69
10-27-2010, 09:37 PM
Track,street..or both?
Cant wait to see the finish.:burnout:

cafe750
10-28-2010, 08:19 AM
looking good so far, your setup of the engine is a little more forward then mine, i had to add an extention to my kickstarter for it to work and not hit the frame since i used the swingarm for mounting the rear engine mount....i talked to a mechanic about rejetting for the street and he told me there really weren't alot of options since the engine relly need to be 'on the pipe' while riding, luckily i don't have too many real long straights to worry about, but i think the 38 tooth rear will help out, along with a 25 front......get a box of 'depends' cause once you get her running you will need them to keep from soiling your pants:banana:

Crim
11-02-2010, 05:40 PM
After much debate on which radiators to use, I decided to just go ahead with the twin KX125 radiators. Mounted them up and they fit perfectly behind the fairings. The lines for them are less then sexy however :/ But luckily they'll all be hidden by the plastic.

I got my RS125 exhaust from Cafe750 and within minutes of opening the package had already cut it up into 3 separate pieces. After minor tweaking the expansion pipe bolts onto the KX125 engine. I haven't welded on the stinger tube/pipe for the silencer yet. I'm still not sure how Cafe750 made his work. I think I need to find a place that sells 1" ID exhaust pipe and add a bit of extra straight pipe here and there to position the can where I want it.

So I rolled the bike out into my driveway, tossed some premix into the tank and cranked her over and off she screamed! No silencer and this thing is LOUD! And to make matters worse I didn't have my cut off switch wired correctly so I couldn't shut her off. Ended up popping the tank up and pulling the spark plug wire. My neighbors love me

So next up on the list is getting that silencer on, and then getting a chain and hooking up the back wheel. Once it moves, then I'll be taking it all back apart to paint the engine cradle and locktite every bolt. :gunner:

Owen.G
11-02-2010, 08:14 PM
cant wait to see the outcome of this. Keep the updates coming. And maybe a video of her driving and running. :)

Crim
11-02-2010, 08:27 PM
Will do, I'll try to snap some pictures tomorrow. Just ordered a carbon silencer from Tyga, hopefully it wont take too long to show up!

Owen.G
11-02-2010, 08:36 PM
thats not so bad. What make is the silencer ?

Crim
11-02-2010, 08:43 PM
This guy here: http://www.tygausa.com/exhausts/82-tyga-carbon-two-stroke-silencer-right-side-badge.html

http://www.tygausa.com/82-221-thickbox/tyga-carbon-two-stroke-silencer-right-side-badge.jpg

Owen.G
11-02-2010, 09:02 PM
nice end can. Its kinda styled like the Arrow. Id say she would sound well with that. :)

Crim
11-04-2010, 02:47 PM
bump-- Updated first post with new pictures!

Owen.G
11-05-2010, 08:09 PM
shes coming along well now. Go out now and look for an rs50 to play with. :)

Dom.C
11-05-2010, 08:29 PM
Nice job, very interesting!

Crim
11-11-2010, 09:39 PM
*bump* updated first post with picture of new silencer!

Crim
12-10-2010, 04:09 PM
Well, a month later I finally got the correct parts in from Kawasaki and the bike put back together. I haven't registered the bike yet, so I only took it for a quick spin down the block and back. I didn't get onto it too hard, but in the upper RPMs it sort of fell onto its face. Not sure if its just the jetting, or the bike wasn't fully warmed up yet. Only a few little things left to do to wrap it up, replace a few crappy coolant hose clamps and re-weld one of the exhaust hooks to make the two sides hold more evenly.

Cafe750 - What size jets did you end up going with? Was it far off from stock jetting?

RS_Patrick
12-10-2010, 07:23 PM
Dont know what you mean by Upper RPM's, but Ofroed bikes dont really rev that high as street bikes.

Also it migh be the Pipe you got doesnt match the CC/RPM range from the Cilinder, if there powerbands dont match you get less power out of it also.

Hopefully its just jetting/mixture though.

Crim
12-10-2010, 07:54 PM
Cafe750 has had good success with this pipe, so hopefully its not too far out of spec for the cylinder. I don't have a tach on the bike, so I was just listening by ear. I know that before I took the dirt bike apart, it wasn't very happy if I tried to ride it before it fully warmed up, so I'm guessing that's most likely the case here.

Crim
12-11-2010, 12:10 PM
*bump* Updated first post with picture and video. :)

RS_Patrick
12-11-2010, 12:39 PM
Cafe750 has had good success with this pipe, so hopefully its not too far out of spec for the cylinder. I don't have a tach on the bike, so I was just listening by ear. I know that before I took the dirt bike apart, it wasn't very happy if I tried to ride it before it fully warmed up, so I'm guessing that's most likely the case here.

Might be a bit lean than on the mixture if does/did that, i take it you did clean the carb etc?

Crim
12-11-2010, 12:48 PM
Yep carb is spotless. I'm sure I'm going to need to bump the mainjet a size or two as I'm running open carb and a freer flowing pipe.

cafe750
12-16-2010, 11:15 AM
Well, a month later I finally got the correct parts in from Kawasaki and the bike put back together. I haven't registered the bike yet, so I only took it for a quick spin down the block and back. I didn't get onto it too hard, but in the upper RPMs it sort of fell onto its face. Not sure if its just the jetting, or the bike wasn't fully warmed up yet. Only a few little things left to do to wrap it up, replace a few crappy coolant hose clamps and re-weld one of the exhaust hooks to make the two sides hold more evenly.

Cafe750 - What size jets did you end up going with? Was it far off from stock jetting?

i'm using stock jetting....the pipe works great so far, the only flat spots i have are between 6500 and 8000, kinda sputters, but once 'on the pipe' i have no high end issues, really screams from 8500 to 13500

Crim
12-16-2010, 12:16 PM
i'm using stock jetting....the pipe works great so far, the only flat spots i have are between 6500 and 8000, kinda sputters, but once 'on the pipe' i have no high end issues, really screams from 8500 to 13500

I forget... are you running an air filter?

cafe750
12-18-2010, 09:30 AM
running a pod filter but during the winter i'm gonna fit or fabricate an airbox under the tank, i think the engine will appreciate it more

Crim
01-12-2011, 05:40 PM
Hmm got in my eletrex l13 lighting coil, it appears to be a big piece of shit. Aside from the fact that the mounting holes don't line up, the winding isn't even completely covered with epoxy. *sigh* Hopefully I can send this thing back.

cafe750
01-17-2011, 04:46 PM
get a moose racing stator
i'll get you the part number tonight, i have the box some where at the house
i also have an new extra lighting coil coil at the house, i forgot i had it, that is supposed to work with kx125/250 if ya wanna try it, it is the older type, pre 2001 and the wiring directions are not the clearest but any mechanic could give ya the right schematics i would think............let me know if ya wanna give it a try

Crim
01-17-2011, 06:48 PM
get a moose racing stator
i'll get you the part number tonight, i have the box some where at the house
i also have an new extra lighting coil coil at the house, i forgot i had it, that is supposed to work with kx125/250 if ya wanna try it, it is the older type, pre 2001 and the wiring directions are not the clearest but any mechanic could give ya the right schematics i would think............let me know if ya wanna give it a try

Damn, that's the one I needed too. I ended up boring out the mounting holes slightly and mounting it up today. Cranked up the bike and my multimeter showed 10v at idle and upwards when rev'd on the lighting wire...so seems to be working for now. Neither the vendor or electrex seemed interested in refunding my money so I just decided to use it.

I got a 4ah battery, but I'm kind of doubtful how well the lighting coil line will actually charge it. I've attached a quick disconnect pigtail to the battery so I can easily plug it into my trickle charger at night if I need to.

Mounted up my 12v rectifier/regulator and started the process of wiring up all the lights. The ignition switch on this bike is perfect. One pair of wires from it are open with the key in the off position while another pair is closed. Then they flip when the key is switched to the on position. I've got one pair tied into the engine cut off switch, and the other one will be the off switch for my DC power circuits.

cafe750
01-18-2011, 12:42 PM
that sounds good, glad its working now.

i have a battery setup too instead of condenser but seems like it doesn't charge well enough to keep the lights going strong but i think i have to recheck my wiring first off. gonna get one of the trail tech 4a batteries this winter while i am tearing the bike down to do a full restore, now that i know all is running right, finalizing the motor mounts and cleaning up all around look of the bike.

the trickle charger is a good idea, will have to incorporate that myself.

now if i can just have everything done by the indy motogp race....i think i have the time now....

btw, i am thinking of changing over to the 2004 honda rs125 body work, i think that would make it way too trick....

cafe750
01-18-2011, 12:52 PM
that sounds good, glad its working now.

i have a battery setup too instead of condenser but seems like it doesn't charge well enough to keep the lights going strong but i think i have to recheck my wiring first off. gonna get one of the trail tech 4a batteries this winter while i am tearing the bike down to do a full restore, now that i know all is running right, finalizing the motor mounts and cleaning up all around look of the bike.

the trickle charger is a good idea, will have to incorporate that myself.

now if i can just have everything done by the indy motogp race....i think i have the time now....

btw, i am thinking of changing over to the 2004 honda rs125 body work, i think that would make it way too trick....

Crim
01-18-2011, 06:33 PM
that sounds good, glad its working now.

i have a battery setup too instead of condenser but seems like it doesn't charge well enough to keep the lights going strong but i think i have to recheck my wiring first off. gonna get one of the trail tech 4a batteries this winter while i am tearing the bike down to do a full restore, now that i know all is running right, finalizing the motor mounts and cleaning up all around look of the bike.

the trickle charger is a good idea, will have to incorporate that myself.

now if i can just have everything done by the indy motogp race....i think i have the time now....

btw, i am thinking of changing over to the 2004 honda rs125 body work, i think that would make it way too trick....

Yeah I went w/ that 4Ah battery from trailtech, along with their rectifier/regulator. I'll let you know how it does once I get it all together. I ordered a pair of 900lumen LEDs and drivers last night for ~$40. I am going to try to run one or two of these as opposed to the stock 35watt bulb headlights. I don't plan on riding at night, just want them as a little extra safety for day riding (and to be more compliant with laws). I've also swapped out all of the remaining stock bulbs for LED's, so hopefully that should help minimize power draw.

-- EDIT --
Oh and if you do the body work swap be sure to post up pictures! Interested in seeing this!

Crim
02-07-2011, 11:43 PM
Created a thread about the LED headlight I'm now running: http://www.apriliaforum.com/forums/showthread.php?p=2737968