I was told that on a high "G" maneuver that the pressure inside the tank exceeds the pressure the muffler tap is supplying. Therefore the air pressure escapes back through the pressure hose and thus draws the fuel away from the carb. Got my check valve from towers today and I'm gonna try it tomorrow and not wait until the weekend. I too have seen a small hole in the fuel line that causes problems every now and then but most of the time a fuel leak is visible and can be detected early on.