The IO540 engine and most fuel injected engines has always been a little tricky to start, especially when warm/hot. They are exactly the same in fixed wing as well due to the heat from the engine causing the fuel in the lines to evaporate which is replaced by air which needs to be replaced by fuel by purging the system (priming) which seems to be differant on every start. On a modern fuel injection system of course this is all taken care of by sensors which know the heat of the engine and the outside air tempreture and feed it all back to the ECU which then calculates exactly how much fuel is needed at the injector.
May be someone could have a word with Frank !!
I also have problems getting it just right, but as the machines get more use (older) they seem to get better ?