There are 3 tricks to learn with an inverted engine.

The first is that you have to get the fuel to run uphill from the carb into the engine when priming. I do this by turning the prop slowly with my finger over the carb until I feel it getting wet from fuel then roll my finger slightly to leave a small air gap and flicking fast at the same time. This gives a sudden jet of air that sweeps up the excess fuel into the crankshaft. Flick it fast a few times to get the fuel spread through the engine.

The second trick is knowing exactly how much fuel to spread through it. Too little and it won't start, too much and it'll be flooded putting out the glow or locking up with the risk of bending the conrod. Practise until you find the minimum necessary amount of prime.

The third trick is that when it's running the idle mixture has to be much more precisely set than you can get away with when upright. It needs to be just barely on the rich side.