Tag: Does it do it when warm AND cold? If so, then it is a tuning problem or a clutch problem. As far as tuning goes, check for air leaks around the carb and backplate, leaking fuel tanks, lines, etc... If it only happens when warm, then you probably need a new piston/sleeve. I have had them wear out from use. When the engine warms (maybe only a minute or two of running) it will bog-down and die when trying to accelerate. The reason for this is because the sleeve expands more than the piston and you lose your compression. Spin the engine over by hand without the glow plug in when it is cold and then do it later when it is warm. It should feel about the same (except for race .21's). If you don't have that "tight" feeling when it's warm, then it's time to fix the engine. You can either buy a new piston and sleeve, or send your old parts out and get them "squeezed" which will bring them back to life!