This is a VERY interesting conversation. And it really does make me think..... that if an engine runs fine while going straight up in the air with the tank several inched below the carb,why would it make a difference while in level flight if you flip upside down? I will say,I too can hear a lean/rich difference many times though while doing this as well as diving and stuff. Not sure what to think,but I do have one question.....

Is it easier for an engine to RICHEN and flood itself like when flying level upsidedown with the tank then higher then the carb then it is to.......LEAN itself out when flying straight up in the air? Perhaps engine are simply more tolorant at "taking" fuel,then "accepting" it?

...maybe this could explain all this,because it sure does seem like both sides are right.