Emergency help needed.

I just installed a fmf titanium pipe and mid pipe. I am getting a ton of back fire do I need to loosen the fuel screw on the bottom of the carb or re-jet it. 01 yz 426

Turn the fuel screw out, to a max of 2 turns. If that does not make the backfire subside, then your pilot jet needs to be changed to the next bigger size, and redeaux.


(New pipe is allowing it to breath much easier, and I bet your air/fuel ratio is a little on the lean side. Good luck!)

Most likely need to raise your needle. Dont mess with your pilot until you get the needle closer. :)

I second Indy's thought, raise needle first, maybe even go to a larger main jet? ( you dont list your current jetting settings?)

The fuel screw will only effect idle and off idle fuel air mix and would change the main jet to a 170 or 175. I put a stock yz muffler on and had to change main to a 175 and that took care of it. The needle may need to be raised if your having a throttle response problem such as having a hessitation. My 04wr450 expierenced the same problem after I changed my exhaust and Raised it one notch to (#5).

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