The problem may be a bad gas cap. Try to run it with the gas cap loosened up or off. If it still does it inspect the fuel lines and replace them if they have any cracking.
The filter will never show to be full when engine is running. The fuel pump is a pulse pump and the line from the valve cover is the sensing line that actualy does the pumping. It is not vacuum. The only way to check pump is remove the line at the carburator and crank engine over to see if it is pumping. You say the unit will not start after it has sat awhile? After it starts does it run ok?