Whats up everybody .I just installed a HMF slip on and a moose racing dyno jet kit. The difference in power is amazing.Today I went to a fire road and had a blast.I have a 13t front sprocket also.This is a whole new bike. But I hear a little backfire when I decelerate from high speeds. I am new at working on bikes. So I followed the instructions exactly.It called for a 128 main ,clip on the 3rd position on the needle ,and idle mixture screw out 3 turns. What could be causing the backfire?Any input is greatly appreciated .I am trying to learn with out blowing up my 09 250s.I live at sea level if that makes any difference.

 

All 4 strokes backfire all the time, its just whether you hear it or not. you put a much louder pipe on your bike, now you can hear it.

Its the unburned fuel in the exhaust burning. If it doesn't backfire at all, theres a good chance its too lean. If you hold it at certain throttle position for a period of time, then leave completely off and you hear a BIG backfire, it MAY mean that particular part of the powerband is rich.

hopefully that made some sense.

 

That clears it up. And no big backfire after throttle for a period of time.Thanks. Again.