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View Full Version : Aprilia Rs125 Jetting Questions



Nils Trubkin
08-14-2015, 05:41 PM
Hi everyone. I got an Aprilia rs 125 (2003), i'm 17 and i had it only for a year so i'm not very experienced with all this bike stuff but i try to do my best.

So yeah, i will start off with saying that i googled and read articles and stuff for a really long time now (few weeks) and i am very confused about the MAIN JET SIZE matter on my bike.
I had recently made a cylinder/piston replacement as my previous one seized up (reason remains unknown more on that in this thread (http://www.apriliaforum.com/forums/showthread.php?306157-RAVE-Blade-killed-my-piston-cylinder)).
I have de-restricted it, and by that i mean RAVE and valve enabled, modded CDI, and a br10eg plug, the CAT is NOT removed, it is inside of the exhaust and i want to keep it that way.

Now for the tricky part. I got a 28! not 34! mm carb. The stock one. My jet settings are 128 MAIN, 70 starter (choke), 62 idle, second needle notch from the bottom i believe, and some random setting i often change on idle mixture screw. I don't want to fiddle around with anything else than MAIN jet, needle and idle mixture, rpm screws.
So the 128 jet is as i believe is on the rich side, because the plug is really black, and i notice some "rich symptoms" like sluggish power in the mid range, and it really becomes super powerful just as i hit 7k RPMs. I just finished the running in of the new engine parts and will do a plug chop soon. I did however make a test run the other day when i (after warmup) put it balls to the walls and got out about 145 kph. That is a bit too little i believe, but not really bad. So my questions are.

1. What do you think about 128 jet on a de-redistricted rs125? Too little/big?
2. Why do i see some people talking about some RIDICULOUSLY big main jets and recommending them for de-restricted rs125 with the 28 mm carb, like 160-180!!! It makes sense to put it on the 34, but not 28.
3. I get noticeably worse results with the 135 main jet compared to 128, which means that 160 jet would totally not work? Or am i missing something?
4. When i will do a plug chop, can i use the spark plug that is used and black (will it become white in case of lean jetting?), or does it need to be a totally new one, or should i just clean it?
5. Can i use the BR8ES for a plug chop test (i got a couple new once) or should i only use the br10eg?
6. What is the top speed i should reach with correct jetting? Can too rich jetting be the reason i don't get above 145?
7. Is there any slight chance that i am running it too lean? I have never seen my plug any near brown could at all, always black.

I only use the Castrol Power 1 Racing 2T since the repair, and try to warm it up a few minutes prior to all the fun stuff. I have a set of main jets for my carb in following sizes 112,115,118,120,122,125,128,130,132,135.

Thank you very much for any help/tips/answers.