This does not make sense. The only way for inertial forces to move fuel to the back of the tank on the down line is if the plane is accelerating more than the force of Gravity. I think most of us probably cut back on the throttle on the down line, letting gravity do most of the work. Since there is drag against the plane, the fuel will pool in the front.

This would be mitigated by the amount of fuel already in the clunk line. By cutting the throttle, you significantly reduce the fuel draw, so you get more time before you're sucking air. I normally use a longer fuel supply line, so I can put a long loop between the tank and the engine. This has not affected engine performance significantly, and reduces the number of deadsticks in a diving maneuver. Another way to address the problem is to take a lesson from the Heli guys and use a 2 oz header tank between the main tank and the engine. This effectively increases the volume of the supply line. When the plane returns to straight and level flight, any air bubbles that may have moved into the header tank vent back to the main tank, and the 2 oz of fuel would support a two to three minute dive. The height of the header tank relative to the carb is not significant, so it can be placed in any convenient location within the fuselage.

Brad