I called them today,,they said it consist of sleeve,piston,gasket set. They say it increases power in the low end to mid range,,top end about the same. I have a full yosh now and dyno jet jet kit and it does OK but want more,,as usual. He says $110 for piston,$58 for sleeve and $12 for gaskets. If that not enough,,he say do portwork and drop in cams,,,but then youre looking at a rev limiter problem. He says no one has a good CDI for it yet. I called yosh,,they HAD one but dont make it anymore,,something to do with Mitsubushi. Anyone tried the Thumper kit from Thumper racing?