MinnFlyer,

I can hear the clunk moving around. I've already tried what you suggested by looking for it but can't see it too clearly. I thought maybe the line inside the tank may have come off.

The plane is a Hobbico Superstar 40 trainer. It was prebuilt. Someone has already suggested that the engine is running to lean which could make it do that. Is that true?

Also, would a worn out spinner, (grooves from starter) cause an off balance condition which would cause vibration?

Thanks.