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i recently installed a42and a158,cut my airbox,removed backfire screen,changed to a twin air filter,msr fuel screw,and removed the exhaust insert.i ride at sea level to1300ft.is the 158 to large?and what is mod that some of you done to the a.p.?thanks alex 04 250x

No, I think you are on the right track.

Are you running the JD Kit?? That needle makes a big difference.

If not run the R needle P/N 16204 MEN 671 on the 4th clip. Its about $ 14 from the dealer.

The AP mod consists of putting an O-ring on the throw arms of the Accelerator Pump thus reducing lag time between throttle movement and squirt.

PM with your e-mail address and I'll send you the whole mod on PDF. Most of us only do the first part with the o-ring. That is enough to eliminate any bog.

Here's the thread
http://crfsonly.com/forum/viewtopic.php?t=9687&sid=9f07b83b37a9c53aaa7a06cec293d175

will the jetting changes open up third.or is that a hotcam install.thanks again