I have another thread open but not sure if anyone is reading it so here it goes again... Bike: 2004 yz450f Symptom: idles ok, at any throttle opening cracks, pops, and backfires work already done: Cleaned carb more than once...no chance of dirt checked entire ignition system even replaced cdi and coil with used unit checked valve clearence and cam timing: perfect performed cylinder leakage test: heres were my question is. It has no leakage as far as the guage goes by % however there is a fair amount of air coming through the air box. I assume here lies the problem. I don't know why the leakage guage reads perfect but I don't think I should have any air leaking past intake valves. Any common problems to look for? I assume its gotta be a valve seat issue since clearences are in spec which means nothing is holding valve open. Im gonna tear the head off tomorrow just to ease my curiousity just wanted to run it past you guys for any more tips or info Thanks!