Why are you able to fill fuel past the point were fuel reaches were the vent starts? The vent should allow fuel to flow up to the top of the tank and then the Fuel lever on the pump should shut off. The reason for this is back pressure build up after you fill to the top of the tank and the vent no longer bleeds off air. Do you continue to resqueeze the fuel lever or does it never turn off? If prperly vented you should only be able to fill to a full tank and no further. Just curious. Mine shuts the fuel lever off at full. Granted I have a fuel cell, but the vent exits only eight inches above the tank.
--Mike