So normally, a 2 stroke engine fires after every upstroke of the piston, but when it is 4 stroking, which is caused by overly rich air fuel mixture, it fires every other upstroke, or even less often, resulting in a significant loss of power and increase in noise. If you like I can make a video of a bike when it is 2 stroking vs 4 stroking, I have one right now that 4 strokes at high rpms and I haven't gotten around to redrilling the main jet yet.