RE: Honda GX31
In this case the engine is somewhat of a dry sump design, so the oil wouldn't seep past the rings. It would however, drain out of the oil tank into the valve train area and therefore leave the tank dry. Same result; no oil being pumped.
Anyway, I'm going to use the engine on my Eindecker and mount it upright. I just won't fly it inverted! Normal positive "G" maneuvers and aileron rolls won't present a problem. Even full size aerobatic airplanes without inverted systems can be flown negative momentarily....
AV8TOR