I tried this exact same setup once. The problem is that the engine is flooding on the first flip of the prop. If you must mount it inverted, you need to close the needle valve all the way, make sure the glow plug is dry and flip it. As soon as it starts, open the needle valve about 1/4 turn before it has a chance to die. A 160FX HATES being inverted. I finally got tired of the routine and bought a Bisson Pitts muffler and layed it on its side, all is well now. It runs rich at 1/4 open on the HS needle, the pump supplies A LOT more fuel than muffler pressure can.

P.S. Or you can start the plane inverted.