The engine that goes inverted needs to be a well broken in and reliable upright engine.

First time you start it inverted, don't.
Start it right side up and run it that way to prove everything is ok. Stop it. Hand choke it, TURN THE PROP TO close the crankshaft opening so all the prime does not drain out whn you set it on the ground.

Plug wire on, flip or spin it, you are running everytime.