Hi IBob, I do have 2 standard wing tanks and the ventilation I have on the fuel caps is the one looking forward to the wInd. What happened to me was that one tank wasn't showing fuel but the other still had 4 gallons. This unequal consum of the tanks happens often, some times it consumes more the left tank some times the right. So I supposed that still having fuel on one tank was enough to ensure the feeding of the collector. To my surprise the collector "reserve" light went on. My theory is that bubbles of air goes from the empty tank to the one that still has. This because of the pressurization of the tank by the vent lines looking forward to the wind. I think that this pressurization is necessary to push the fuel to the collector. My solution to this problem was to install fuel valve selector that allows me to choose right,left and both tanks. When I see that one tank has less fuel than the other I just change the selector.
Happened to me. A very scary experience. The light went on though I had 4 gallons on my right tank. I had to make a emergency landing with the engine off. I am convinced about air bubbles blocking the fuel.
