I mean the valves in ur engine! and the air screw that adjusts how much air goes to ur carb, u might need to adjust it, look at ur manuel to see how many screws to adjust it.
*Valve adjustment:
http://www.youtube.com/watch?v=s0K-ytyjOFg
*Carb air screw:
http://www.youtube.com/watch?v=iNkeLS2HFtw