View Full Version : Aprilia rx 50 to 70 project

08-05-2012, 02:58 AM
hi everyone, I have a
07 aprilia rx 50 I bought about a year ago. The bottom end was gone and the whole engine has been rebuilt by (FIREFOXRACING) I had a 70cc bore kit fitted. carb hasn't been set up for borekit. What's sizes jet is best? any advise for me?

now the bike so you know what I'm working on!

2007 aprilia rx 50.
D50BO engine with 70cc borkit.
2005 model radiator. (old one was smashed and got this for 20)
Standard exhaust with all restrictors removed.
standard air box and filter.

Bike is in peices at the mo as I'm spraying bottom of forks, swing arm and bars white. I'm looking for some cheap sm wheels??? brake calipers will be green along with green chain runner, will respray plastics red green and white. This bike is sorn at the mo will I be able to get it back in road with the borekit

08-05-2012, 03:23 AM
need to know what carb you have too

08-05-2012, 09:53 AM
theres lots you need to upgrade when going to a big bore kit espically if you want it to be reliable and fast

stock clutch is likely to slip or at least burn out quick with 70cc kit, you need upgraded clutch springs so it can nail down the extra power and upgraded clutch plates so they dont burn out as quick (if you want to buy a decent kit then id advise the polini heavy duty clutch kit from adrenalin pedstop website - it can take alot of beating)

bigger carb, 21mm would be ideal

race crank, big bore kits put even more vibration on the crank bearings putting even more strain on the crank itself which is likely to sheer off on the flywheel side (this is why race crankshafts such as the doppler ER1 crank have a bigger crank bearing on the flywheel side). you need at least upgraded crank bearings but idealy you should get the doppler ER1 crankshaft which is very reccomendable as it can safely cope with 18000rpm and increases performance slightly but gives you that peice of mind that the big bore kit isnt going to shake it to peices after just a few miles

stock air box is good, performance filter sheets help

0.35mm reed petals, the stock ones will flutter very easily at higher rpms

you may also need to go up a tooth on the front sprocket if it over revs in top gear

stock exhaust will hold that set up back alot, a performance exhaust will make a world of difference as the stock exhaust is designed for stock 50cc cylinders with a smaller carb. exhausts to look at are: giannelli leo vince Arrow Turbo kit jolly moto

05-01-2013, 08:09 AM
Hi guys thanks for your replies!

So basically the project got put on hold while I rebuilt a nrg but I've now started sorting the rx70 out.
I got the bike started today but as soon as she started she over revved and I killed it just cause its freshly rebuilt and I don't want it screaming itself to peices. I'm guessing the cause for this is to much air getting in?
I also noticed while stripping the carb it had a 107 main jet? I'm guessing this bike was f**ked about with before I got my hands on it. does anyone know what jet size I should be using? other than it over revving it seems to run alright but can't really tell yet. Any help would be massively appreciated.



05-01-2013, 03:16 PM
What carb do you have on it Rich? What is the make of the big bore kit fitted? I would start at 100 and work my way down in 2's untill it runs correctly. Then do a plug chop to make sure the mixture is spot on (plug should be coffee colour).

You will need to play around with the air mixture screw on the carb to get it running right aswell.

Top Tip when running in a new top end : Run an extra 100:1 premix in the petrol to prevent seizure.

05-03-2013, 03:54 PM
it's the airsal 70kit and its running good now! just redoing all radiator hoses and so on. i need a performance pipe as I can here the standard one hold it back.

I have a stage 6 exhaust for a piaggio nrg I can't remember model but its for the 70/80 kitted nrgs is using this exhaust a possibility or am I going to have to by a new full system?

the cause for the screaming mentioned on my earlier post was the throttle get a jammed and not returning all the way LOL but cheers for advice, let me know what you think about the exhaust!


05-04-2013, 08:31 AM
You need a exhaust matched to the barrel you have...so no, not a nrg pipe. The best exhaust around imo for the RX/SX/SM am6 bikes is the Tecnigas Anox, Adrenalin pedstop sell them. I have first hand experience with this exhaust and it makes one hell of a difference on 50cc and 70cc. They're around 150.

05-04-2013, 04:24 PM
If you want to fit a 70cc+ kit heres a list what i think you need to upgrade:

70cc Big Bore Kit complete with head.
Bigger Carb.
Stiffer reeds (preferably a Malossi set of 3 difrent thicknesses)
Suitable Sparkplug
Performance Exhaust suitable for more CC's
Stronger Clutch spings.
for AM6 engines i recomend changing the Crankshaft also, but if your bike is a 07 it does not have a AM6 but a Derbi D50B0 engine, if it has a AM6 engine your bike is from 2006 or earlier wich you can find out from the frame number.

05-06-2013, 12:21 PM
cheers reply, I've got it jetted right for moment but will take your advice on the reeds and exhaust! So are you saying if I have the d50bo engine I don't need to upgrade my crankshaft?



05-08-2013, 05:22 AM
if it has the Derbi D50B0 engine you dont need to upgrade the crankshaft, its better though because a race crank can handle higher rpm's and gives a bit higher performance due to being a full round crank.

If you got the AM6 engine your bike is not a 2006 model, and i seriously advice you to swap the crank for a Doppler ER1 as the stock AM6 cranks are know to snap with 70cc+ setups, you can wait till it happens, but big chance that more than just the crank gets damadged from debris and the crank sudenly being oy of balance.

05-11-2013, 04:17 AM
my rx is 57 plate so it's a 2007 model, do you know of this Is the d50bo engine or am6?

does anyone also know if the derbi senda fairings/plastics fit the aprilia rx50?

Also back to the exhaust, I managed to try the stage 6 exhaust for the NRG on the rx and seemed to run really well.. I'm seriously thinking of slicing this exhaust up and welding it to fit. Please give your opinions on that one!

Ill give a full update later or tomorrow maybe even some pics?



05-11-2013, 10:39 AM
The Plate doesnt tell you anything about what Modelyear the bike is, people here keep making that mistake.

The Modelyear is the 10 position of the frame number, a bike could have been for 2 years in a shop before i got sold, or in some cases you can get next years model already by the end of the previous year, for example someone here bought a 1999 model RS50 that was already sold End 1998, that doesnt change the fact that its a 1999 model.

AM6 says AM6 on the engine case near the sprocket, while the D50B0 says D50B0 there. there also visualy difrent, on the D50B0 the clutch lever sits on the side of the Clutch (right hand side of engine) while the AM6 has the Clutch lever on the other side (left hand side) and uses a rod trough the gearbox to operate the clutch.

05-14-2013, 12:35 PM
Yea I'm pretty sure it's the D50BO engine as the clutch is on the right hand side.. Cheers for your help I'm sure ill need more advice as the project moves on.. I'm trying to get some photos on here but can't work out how to on the iPhone :S

05-14-2013, 05:25 PM
Androud here mate :p: HTC One X, so cant help you with that part, i just upload pics to Dropbox or directly to my PC and from PC to Photobucket.com and i place the link here.

Atleast we now know you got a Derbi engine, makes it a lot easier helping you wen we know what we are talking about (you might want to edit it in your firts post)

05-15-2013, 06:59 AM
no worries I think I have to download a app or something will try on the laptop later. Yea cheers for the help with that again plently more for you to give advice on...

so the bikes pretty much together just waiting on a few connectors for my radiator hoses. i have had to reroute my radiator hoses as I have 2005 model radiator instead of the original as the original is 180 and I got this old style one for 20 but the out put at the bottom faces the exhaust outlet instead of straight down so I've had to come up with a idea to get the hoses to fit with out going up hill.. you will see what I'm saying when the pictures come up, but the question is.. Is will this work? With out my bike over heating?

06-17-2013, 11:29 AM
hi guys still can't manage to get pictures on here, will wait till completely finished and I'll get them all up at onces.
But any way... I've been doing some testing and I'm pretty sure the clutch is slipping so stiffer clutch springs it is, does anyone know where supplies? i have looked but only found on eBay and they were some random make so decided not too.
Also anyone have experience bleeding these sh!tty brakes? just can't seem to get build any pressure, I've have the master cylinder in bits and all seals are perfect so no idea why I can't get them working any help is fantastically helpful

06-17-2013, 12:24 PM
What jet you running on that airsal 70 kit as I'm gonna buy one but want a idea of what jets to buy

And yeah there crap take the mick to bleed I think

06-17-2013, 01:49 PM
Get someone to help you to bleed, one bleeds and one pumps.

open nipple, sqeeze the pump, close nipple, and let the pump come back up, and repeat till no air comes out of the nipple, i advice you to use a transparent tube and a glass yar to bleed into as the brake fluid is highly caustic and if it comes onto plastic or paint rince it with water right away.

06-18-2013, 11:15 AM
I believe it's a 100 and something main jet with open pod style air filter.

Cheers Patrick but I have tried that for hours with a mate and still no pressure.

New battery came today filled it up and connected it all up turned the and yep the fuse went (the one on the positive wire)
any typical problems for this bike or am I gunna have to search for the cause

06-19-2013, 02:24 PM
electrics sorted. Just need somewhere to buy clutch stiffer clutch springs? and a performance exhaust

06-20-2013, 03:25 AM
electrics sorted. Just need somewhere to buy clutch stiffer clutch springs? and a performance exhaust

Can get all that off pedstop and ebay.

06-20-2013, 11:02 AM
Vsmotoparts is also good

06-21-2013, 05:49 AM
or easyparts.nl or directly from Malossi

I wouldnt buy parts of Ebay...

01-05-2014, 08:13 AM
This project has been left for a while as I have bought a yamaha dtr125 but finishing the rx as we speak, will have pics up when finished. Thanks for all your help everyone i know it's been on and off but this time it's getting finished!

01-05-2014, 08:40 AM
This project has been left for a while as I have bought a yamaha dtr125 but finishing the rx as we speak, will have pics up when finished. Thanks for all your help everyone i know it's been on and off but this time it's getting finished!

Get some pcs up of the rx and the dt love them dts