Followup question - when in sustained inverted flight with engine and stock tank setup (i.e. muffler pressure to the vent tube), are we pumping raw fuel out of the tank and through the muffler? Vent tube is bent upward and nearly touches the top of the tank but the whole tank is lower than the carb when upright. Fly inverted and the tank is now higher than carb and much higher than the muffler.

Does the higher pressure in the muffler prevent the fuel from exiting?