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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