The trick is in perfecting a new priming technique because with an inverted engine the carb is also inverted (obviously ) so fuel tends to just dribble out instead of running down into the crankcase. But spinning it over with the starter with your finger blocking the exhaust can force too much fuel through and flood it. This of course is bad news for an inverted engine, first because it drowns the plug but mainly because you can get a hydraulic lock.
When you get the technique right you'll find it'll start just as easily as an upright engine.