when you said you use a racing mixture what is it. Usually a good mixture is 32 to 1. The difference between 2 and 4 stroke engines is a 4 stroke has for different possitions and valve openings. It starts out with intake (piston goes down), compression (piston goes up), power stroke (piston gets force down), and exhaust (piston forces out exhaust). Then it restarts. A 2 stroke has intake, then it ignites at the top gets forced down opening the exhaust hole while taking in gas. so it ignites every time it goes up were 4 strokes fire every other time.