ORIGINAL: Campgems
First, the clunk doesn't need to reach the front of the tank, nor do you want it to as it will sometimes stick there. When you are in a dive, unless it is a dead stick dive, you are going to be dropping faster than the pull of gravity. IE 16 ft per second per second. The fuel is going to be like anything else, and floating or pinned to the apparent top of the tank. Static test, IE holding the nose down should result in a dead engine if held long enough. That is not going to happen in the air though.
Don
this is incorrect, the fuel doesnt stick to the back of the tank. the only thing that keeps the engine going is the fuel in the fuel line. this isnt a problem (unless your a mile in the air) because that fuel in the line will supply the engine for around 15 seconds. that will put your plane in the ground if it takes that long for you to get down, so it isnt a issue.
dont believe me? next time you are running a engine take the line off the carby, it will run for about 5 seconds before dieing thats with no fuel line. now add 6in of fuel line and it will run for a while, long enough for the plane to level out and get fuel again