Thanks very much for taking the time to respond guys. I thought it may have been a cold engine, but it happened on the second and third flights of the evening also. I should have tried to gun it on the ground after the flight to see what it would do. I'll try that next time out. If it persist I thought I might try the new WJ71 carb I just bought for a spare engine. Also, what are the symptoms of a bent crank? My spinner looks like it a has slight wobble when the engine is running.