I've got an airplane with an inverted two-stroke AND the fuel tank is a good inch above the carb. It runs fine, it took a long time to get just right. They will run ok, BUT the margin of error for the needle settings is VERY narrow. Also, try a hotter glow plug.

Two strokes are harder inverted than four-strokes because the glow plug sits at the very bottom. The oil can pool down there and cool down the plug.