ORIGINAL: Richard L.
This is a YS 4-stroke with built in pressure regulator, so there is no need to clamp the fuel line while fueling. The regulator will not allow fuel to flood the engine. Otherwise, we would have used a third line for fueling and draining.
Richard L. isn't this statement only true when the carb is fully closed? If my carb is slightly open after a flight the fuel sometimes burbles out the carb.