1 problem of mounting the engine inverted on a 4 stroke is they can easily flood, especially if the center line of the tank is higher than the carb, fuel will siphon into the carb, right down intake and cause a nasty hydro lock condition, I've managed to blow more glow plugs and spend more time draining my 120 fs mounted inverted than actually flying it, until I lowered the tank to help prevent this from happening, or you use a perry pump, or a loop to form a trap and keep it from flooding.