I had a PC-9 ARF I finished last year that called for the engine to be inverted and I ran into many of the same problems that are described in this thread. The engine was constantly flooding and would not run for very long. When I mentioned this problem to a friend of mine he put on "Fuel Filler" and it solved all of my problems. The Fuel Filler is installed in your cowl. I just ordered a few of these from Airborne Models to keep on hand. The link to the fuel fillers is below.
http://ecsvr.com/abm/ShopDisplayproducts.asp?Search=Yes

Indy Park Flyer