[bour]

Fuel injection or Carburetor? if fuel injection then you need to look into getting a new one if carb then just needs a little tuning.

 

[charly]

Your spark plug timing could be off or you have fuel left in the piston cell and it added more.

 

[imported_burn]

Hey Theo Good answer... Check your timing... the chain could be streched causing the timing to be off! Bad fuel, bad spark plugs!