Recently I swapped over the engine (80c 2 stroke sat for 3-4 months) to another bike. Once I got the bike running it ran good when the engine is cold (all the way to 30 mph/maximum rpm which is the highest I got it to go) but once it warms up the engine breaks up and has no power at higher speeds and only tops out at 23 mph (its only running at about 1/2-2/3 of its maximum rpm). I cleaned the carburetor and cleaned the oil fouling from the spark plug (don't have another one on hand). Bike is fine at lower rpms.