This bike runs great all the way from 0mph - 38mph, no 4 stroking, no hesitation, pulls hard. I believe I'm getting everything out of this motor that it has. The problem is it will only do it without the air filter. Even using just one layer of panty hose with a rubber band for an air filter it drops 5 mph and 4 strokes. My question is, is there anyway I can get 38 mph and run a GOOD air filter? If you need anymore information just ask. Thanks.