ORIGINAL: ameyam
Actually, I and many other at my field have had problems with inverted 2C engines. It has got to do with starting but also with tuning. We found that it would rich at full tank and lean out as you go through the tank. On a 3D airplane, this was an issue.
Apparently others had the same problem. I couldnt keep that engine running at all. When I finally gave up, one of the more experienced members came up to me and told that he had the same issue with the same airplane. So much so that he does not buy airplanes with inverted engines. He takes them if the engine is at 45 or 90 Deg
Ameyam
If you look at the relationship of the tank to the carb, you can usually solve those problems before you have them.
Why would a specific airplane "always" have the same problem? Think it might be the design? The tank too low or too high?
I very often use uniflow tank plumbing. However, with my H9 Corsair (engine at 9o'clock) I had a siphoning problem. Rerouted the lines and had a draw problem. Actually, it was a priming problem as the lines were not only empty but the carb could barely be finger choked. So I got re-did the plumbing to the usual arrangement. That airplane went from a "leaky" problem, to a "dry" problem, to no problem. The H9 Spitfire engine is straight down. When I was building it, the Corsair was in it's wet phase. The Spit wound up having the same problem as the Corsair when it had the same plumbing. And again as well. In both, that very large tank winds up with enough fuel head over the carb (90degree or inverted) to cause headaches.
Bottom line is that every 6 o'clock engine I've got starts and runs great. But since I like to have the option of uniflow, I usually don't go for 6 o'clock as 1st choice.
There was only one engine in 50+ years that I never got to run straight down. OS produced a 4cycle "lightweight" awhile back and it's downdraft carb was basically a guaranteed flooded engine producer when pointed toward the sky. They did advertise that it started great dry. The opposite was also true. It was a disaster to start wet. If it did, you might wind up sending it back for repairs. They did send me a new replacement. I ran it upright and put it back in the box. Someday I might try it side mounted or upright. Otherwise it stays in the box.