Hi:
Inverted engines can be difficult to start unless you follow a few basic steps. The problem comes from getting fuel into the glow plug and putting the fire out before you even get started! Most people have a helper hold the plane inverted when it gets really nasty.

Be sure that the tank is a bit on the low side so the fuel will not syphon into the carb. When fueling up clamp the line to the carb - or better yet fuel up using that line. Once fueled, do not prime or choke the engine. Use a starter and just crank it until the fuel flows in a normal fashion and it should fire up right away. A HOT glow driver is a must.

If all this fails, then get a buddy to hold the plane inverted.

If you follow these steps you should have no trouble and will have a clean installation.

Phil