One problem I see with your theory, our engines are not fed by a gravity tank for there to be any pouring involved. On a motocross bike the tank is above the motor and fuel line goes down as with the fuel so air needs in so it doesn't vapor lock like you describe.

On a nitro RC the fuel pick up is well below the inlet to the carb. So for the fuel to go up hill and threw all the twists and turns some ppl have it needs a pressure to push it. Hence the pressure line. If you had no pressure line the motor does not have any suction so it gets no fuel. And sine the pickup is below the carb gravity is factored out. Why do you think air leaks cause tunic issues? Extra air is getting in and and tank pressure is reduced so you ge less fuel to the motor. The pressure line is basically a simple fuel pump on these cars.

It's nice to have a civil debateabout our opinions online for once. no name calling or what not.