Not that i think it is valve clearences but how did you check the valve clearences and what were they?? where was the piston when you made these checks. The next question is have you checked the venturi and main jet are clear. Can you please tell me do you prime the engine with fuel or is it equiped with a choke? If it has a choke does it close properly when you place the throttle in the start posistion? When you cleaned the piston and valve were they covered in thick black carbon (big pieces of dry black stuff)?
