If an engine doesn't like being upside down it's usually because the fuel-tank is too high.
Because the carburetor of an inverted engine tends to be much lower than that of an engine mounted upright, its very common to find that the inverted engine runs rich at idle -- making it impossible to get a reliable low-speed idle without the engine cutting when the throttle is opened.
This is why a hot plug like the OS-F can help, it allows the engine to tolerate the much richer mixture that comes from having the tank higher than the carburetor.
The best solution however, is to try and lower the tank.
I had this problem with my P51D Mustang with ThunderTiger 91FS engine. I ended up replacing the standard tank with a smaller one that could be mounted lower in the fuselage. Now it idles like a dream, as you can see at the end of this video:
P51 Mustang wheels-up touch and go
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