After 3 weeks of messing with the carb and changing jets, adjusting the needle etc i still cant get my quad to run good. Stock on the 250x is 35 pilot, 125 main and the needle is in the middle at slot 3. Right now my carb is 42 pilot, 140 main, and the needle is still on the stock position. It breaks up on the low and mid range, blows a lil black smoke, but it also backfire jsut a hair in higher rpm. I am totally lost on how i should jet this thing. my mods are

White brother race cam
40 over high comp piston
stiffer valve springs
fmf exhaust
uni air filter with air box lid removed.


So any help or ideas, anyone with a modded 250x out there with good jetting let me know what ur using.

 

your jetted to rich. go back to a 40 piolit, and try a 135 main jet and one clip richer (one slot down)

 

Yes that is exactly what I was going to say, to rich. I would guess 40 pilot and a 132, but we are close. I hope that helps.