Captain John, how is the engine mounted in that airplane that "misses" when inverted? I have seen people have cylinder UP mounted engines have this problem if their mixtures are set too rich. Fuel can accumulate in the crankcase during upright, (and cylinder upward) flight. When they invert the plane, the engine goes rich because the accumulated fuel then gets into the mixture flow.

I had a friend that had this problem recently. He had his low end set too rich, and it would occasionally burble at around half throttle. He would fly around for a while, then go inverted and the engine would puff out a bunch of smoke and go rich. Setting his mixtures properly solved the problem.

Other than that, tank placement will have no difference with the pumped/regulated Walbro carb or it's copy cat cousins.

AV8TOR