I think the engine gurus will need more info... is it stopping when running at full throttle or at idle? Does it gradually slow down and start blubbering or is it a quick death? If you start the engine and let it run, then hold the airplane nose up at full throttle, do you hear a slight increase in RPM or does it just die? When it dies, grab (carefully!) the head...is it really, really, really hot or just barely warm?

Suggestions... replace the fuel line in the tank and to the needle valve/carb. Adjust needle so that there is a slight increase in RPM when held nose up at full throttle and it continues to run like that. Once you get the needle adjusted, you shouldn't have to adjust it more than a few clicks in either direction.

Wish I could help more...