The float valve is the most likely the main problem. I have seen the problem several times before. stuck closed, no fuel into the carb, open carb floods. By the way, if the throttle butterfly is closed and the carb is flooding, gas will leak out the throttle shaft in any carb. Doesn't mean anything is wrong with it.
But you could have a secondary problem. The tank requires a vented cap. Without it a vacuum will form in the tank as gas is used up. This happens very quickly when the tank is full but takes much longer when the tank is low on fuel. When the vacuum gets higher than the pump spring can push, no more pumping. Even a vented cap can become blocked.
How did fuel magically appear in the filter? In either case, when the fuel pump can't move fuel the diaphragm bottoms out against the spring. even with the engine not turning the spring is pushing on the diaphragm. If the stuck valve opens due to temp change or vibration, or the vacuum in the tank is relieved, the diaphragm will then be pushed up by the spring pumping some gas.

Last edited by Jim Sears; 05/19/2013 12:02 AM.