Re: some problems and questions
You haven't told us what kind of engine you have but we'll assume it is a 2 stroke, Chinese kit. If this is correct you do not have an air/fuel mix screw. The only external adjustment on the carburetor is the idle speed screw, left side of carb. The air/fuel mix is determined by the position of the 'C' clip on the needle valve inside the carb. There will be several grooves cut into the upper end of the needle. The stock (factory) position is usually the second or third groove from the top. The higher you place the 'C' clip the leaner the mix; the lower, the richer. It sounds like you might be a little rich due to the black plug and piston. Reposition the 'C' clip one grove up and try it.
Also if this is a new engine you'll notice improved performance as you accrue miles on it. They run better as they age. You didn't say what fuel/oil mix you are using( ignore the kit manual that might tell you to use 16:1) we recommend starting at 24:1 then moving down to 32:1 after a few tanks of fuel.
As for head bolt torque: Shoot for 110 to 120 inch pounds and check them after the engine has reached operating temp a couple of times. Do not over tighten them or try to get them tighter afterwards. Go for 80 to 90 inch pounds for the plug and don't try to remove the plug from a hot engine. A good antiseize compound lightly applied to the plug threads will be a benefit too.
Good luck. Let us know how you're doing.
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Last edited by 2door; 07-19-2010 at 09:45 PM.