Sitney ... the trick in getting engines to run well upside down is some patience in tuning. My Aresti was running on a Saito 72, one of my pals was with an OS50SX and then an ST G51. We do not have any real starting and idling problems. One thing I found out is that the first time you start the engine for the day is always a problem, being inverted the fuel will not feed properly. Use an electric starter or flip her upside down to start her. After the first flight she will always fire up.

As for tuning I found that you need to run the engine leaner than when its upright. Means if upright you open the needle for 2.5 turns then when inverted its about 2 turns.

Priming should be only one turn or so ... do not do more if not you will flood the engine. Using a refueling valve helps when you fill up, it will ensure hardly any fuel goes into the carb as you fill up.

Take some time to tune the engine and it will run well! Mine did as I invested in some time. All my 2C or 4C engines run well inverted.