2009 yz450f popping with fmf exhaust stock header. help

hey guys i recently got a 2009 yz450f and im new th 450s its popping while riding and anytimei let off the gas. i was thinking valves but its super easy to start. any help would be greatly appreciated.




You can check for exhaust leaks. However, popping is to be expected on a race bike with an open muffler. If the seller gave you the stocker, put it on. It will be quieter, pop less and be just as fast. Time yourself on the track to compare.

Properly adjust your fuel screw using the 'how to set your pilot' post at the top of the forum.

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