If you haven't tried to lower your low end needle, this is a good place to start. I have a 100 mounted inverted in a Cap 232 sport. I have about 5 gallons through it, and it now idles reliably at about 1800 RPM.I can make it idle lower than this, but 1800 is where I don't have any problems with the engine stalling. I would try leaning the low end needle, and then setting your idle as low as possible while remaining reliable. Fly the plane in this configuration. After a gallon or so, see if you can bring the idle down some more. Once these engines are fully broken in, they idle like a harley, even inverted.

Allan