Hey Cen i tried to reply to your email regarding this issue and it returned to me saying your email address was bad if your carb setting what you said "I tuned it high end: two turns out from fully closed" that is way to lean and your over heating your motor which in turn is causing your motor to smoke Here is the factory settings for that motor Top end-3 turns out Bottom
end---4 in from flush that will be for a good running motor.