Glow engines can all be problematic when trying to run them inverted. That's because the glow plug becomes the lowest point in the fuel system. When the throttle is closed to idle, liquid fuel can foul the plug, putting out the fire. An otherwise fine-running engine can run poorly when turned inverted. The best way to avoid inverted-running problems is to get the engine well-tuned when upright, and then use an on-board glow plug battery pack to power the plug when the throttle gets below about 1/3 or so. That will almost certainly cure the difficulty.
Mounting the engine at such an angle that the lowest point will be the exhaust valve allows excess fuel to drain out of the engine and not flood the plug. Helps initial startup as well as running. FWIW. Good luck.
Sincerely, Richard