Richard, Oops, I missed your statement that you get the leak down even when the fuel valve is shut off. My bad.
In normal operations, your fuel should not have all that much overflow back to the wing tanks - I doubt that's your problem. When the engine is running and up to flying rpm, the mechanical pump moves way more fuel than the engine needs. This does build up some head (excess fuel) in the header tank and the higher the "head" the faster fuel flows back to the mains. I've never seen the floating cork fuel gauges go all the way to the top - they're not designed that way. If you have an early Coupe, it may have the 5-gallon header tank. After the war, they switched fairly early to the 6-gallon header tank, I think. When you shut off the engine, that extra fuel "head" will drain out to the level of the overflow intake. The fuel level should stay at that level forever. But, we have a lot of Coupes with slow leaks in the carb and owners who shut off the fuel valve. Humm, if you have leakage with the fuel valve shut off, I'll have to defer debugging that to the mechanic type guys. Ed
