If you would please, take a look at the attached schematic and tell me why I'm venting fuel overboard during flight. For calibration purposes, here are the essentials:

Plane - 80" WM Extra
Engine - FPE 3.2 gas
Tank - 800cc (27 oz) rectangular, mounted on the CG
Vent exit - through the belly of the fuse, just aft of the main gear

The check valve, tee, and fuel dot in the vent line were not there originally. I noticed the venting problem and added those pieces, assuming it was a "siphoning" problem. This after trying several configurations of vent line, to include turning it 90 degrees, with the tube facing forward as shown in the schematic. The check valve has slowed the rate at which fuel is venting, but it has not stopped it.

This is my first gasser, and at first, I thought it might be "normal". But after talking to some very experienced modelers who have built literally dozens of gas powered planes, I don't think so... they're saying I shouldn't even need the check valve. I can live with this problem, but just don't understand why it happens. There are absolutely no tuning or "flyability" problems with the engine... it starts and runs flawlessly. I am considering the installation of a smaller tank, but I can't imagine that it would have any effect on this problem. (I used the stock WM tank that came with the kit, converted to gas with appropriate tubing and stopper. It was intended to feed a large glow engine and is really about twice as big as I need.)

Your comments and suggestions are very welcome!