Just got my 04waroir back. Had a 12:1 piston installed. Took it up the street, it backfired and popped. the guy that did the work said he change the jet to a 155. I think maybe i should change it to a 160. haven't checked the air screw yet. I'll bottom it out then turn it 2-2 1/2 turns out. any suggestions?
k&n filter
hmf slipon

 

I dont know your elevation but you might need a bigger jet...Im assuming your using a dyno jet...also, turn out the screw 3 turns....you might also need to go to a bigger pilot. Try to ride around and check your plug...that will lead you in the right direction.

 

Thanks for info. i think i'll go up about 5 mm jet size each time and go from there.