The reason I posted is that it died on me after a long inverted to straight down dive. After it leveled out, it died and I overshot the runway into an old fence covered with honey suckel vines. Lucky no damage was done. I pulled the tank out today and the clunk was at the front of the tank still, I suppose due to the sudden stop into the fence. I changed the clunk tube to a smaller diameter tube but it still won't fall to the front of the tank in a downward attitude. I'll try what you say about the test of how long it will run after it loses it's fuel though. I'm still prone to blame it on the fuel delivery system.