ok i have a 00 400ex with a biggun full system on it .. about 1000ft above sea level im currently running the needle in the stock position, with a 42 pilot jet, and i tried a 158 main jet, and it seemed to BACKFIRE ALOT when i tried to rev it up a little bit, its really annoying me, and i need some help, so help me out.. please.

 

Take your air box lid off and see what happens...

 

i have my airbox lid off, and my snorkle

 

what was your throttle position when it pops and where does it pop-intake or exhaust?