Found out exactly why the engine had flooding problems. It wouldn't start reliably when new and especially when new and upside down. And because it wouldn't, it's "upside down" carburetor pipe caught all the fuel that came in instead of letting it drop out. That's engine being upside down and being finiky on getting just the right conditions to start were the reason for the flooding problems.

If the tank height was a problem with that engine, it wasn't with the replacement engine. Which was a 2cycle. Both engines have the carb in the same vertical position above the crankshaft right at 1" above. What they don't have in common is the 4cycle's pipe that runs from the carb to the engine. The 2cycle's carb is directly over the crank and the intake valve (which is directly underneath, in the crank itself). The 4cycle has what was working as an accumulator pipe that the 2cycle doesn't have. Two cycles don't have those long delivery pipes. And when I replaced that 4cycle with a 2cycle on that airplane, and without doing a thing to the airplane and plumbing other than unplugging the hoses from the 4cycle and plugging them to the 2cycle, the 2cycle never once flooded. Tank location causing flooding? Probably not. But if it was, then you could add another difference to the list on the 4cycle side. Need different tank locations that 2cycles to keep them from being prone to flood.

Hey, it wasn't my idea that some 4cycles don't work upside down. It was a gaggle of 4cycle guru's collective judgement. I've only had one 4cycle and it was backing up their belief in spades. And I'm passing on to a newbie what another (4cycle) newbie encountered and then was told. I've only had one and it was a pita to start while upside down just like all those experts told me. When I later ran it upright, it started almost every time and when it didn't, it didn't then fill up that collector pipe.

Having fought the "model airplane engines don't start good upside down" fight for years........ yeah, I know it's not really true. When they're upside down, you really have to have the starting technique down pat, and it starts from when you fill up the fuel tank. But what I'm saying is that what looks to me to be a standard layout 4stroke appears to be vulnerable to flooding from it's design. And they all look like that. So......... 4strokes seem to me to be even more critical to having a good starting technique down pat, and you'd better get it right for sure with a 4stroke.