Last week when I was at the field a new engine problem creeped up on me. When i'm tuning the plane by holding it vertically the engine has fuel for about 10 seconds and then fuel just stops running to the carb completely. What could be causing this? I changed the glow plug checked all the crankcase bolts everything seemes tight. The engine is a .40la and is about 3 years old. Could the motor just be worn out?