i jus got a 400ex thats buitl up pretty well and was just rebuilt this past summer with a 440 kit in it......i jus put a larger pilot jet in it because wen i let off the throttle it would pop really bad. now the popping is moslty gone but today i went for a top speed run against my buddy's 350 raptor and wen i got to top speed the motor just kept cutting out a little bit, just enough to notice, could this be a jetting problem? thanks for any help i can get

 

Assuming you werent bouncing off the rev limiter, sounds like you need a bigger main jet.
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