ORIGINAL: da Rock
Wrong both ways. The only thing affected with any of them is the starting. And once you've got the plumbing right and figured out what they need for choking (some don't need it and work just excellently well, some do and don't work very well) they usually aren't much problem.
Exactly!
I run dozens of 2C and 4C engines inverted, and any problems tend to boil down to plumbing or mistuning.
Even tank height differences only affect starting when the engine is on the ground, usually due to minor fuel siphoning.