pull the carb off clean everything and check to see if the seal is ok then put it back together, check to see if the head screws ore tight if not pull the head off and clean it look at the piston to see if its ok put a few drops of after run oil on top of the piston and work it in by turning the crank, then put it back together, reset the carb back to stock setting which will be a little rich, then adjust from there. I would try this before buying a new engine...