I'm having a problem which seems to defy physics and logic, or maybe it's just me, there must be a simple fix for this. My aircraft just does not want to feed fuel from the left tank, the right tank feeds fine. Nothing is obstructed or kinked, the fuel cap vents are clear, and the finger strainers are perfectly clean.

Upon some taxi testing the other day trying out the new Shock Monster tailwheel, I started with equal fuel, about 3 gallons in each tank. After a number of high-speed taxi runs, I noticed the fuel visible in the vent line was below the wing, confirming that the right tank was completely empty, and the left tank was still showing the same as when I started. I shook the plane by the wingtip and jiggled the fuel line around quite a bit, still no fuel flowing. Back in the hangar (my garage) I did several rounds of draining the fuel from the lower sump to the point that the header tank was partially empty, then adding fuel to the tanks a gallon at a time to observe the flow into the header tank.

Each time I put fuel in the left tank, it would not flow into the header tank, unless I disconnected the rubber hose from where it connects to the metal portion of the line. Gas would immediately gush from the hose out of the wing tank, I would quickly reconnect the line, and then flow quite freely into the header tank and begin cross flowing up the vent tube and fuel line on the right tank. Upon draining from the lower sump again, the right tank would drain completely as the header tank went partly dry, but the left tank still had the original amount of fuel. Repeat the process, as soon as I disconnect momentarily the rubber hose from the metal line, fuel would flow. Over and over, fuel would flow from the left tank only momentarily. As soon as fuel stops moving into the header tank, the left tank stops flowing and the right tank works fine.

As can be seen in this photo, this is the configuration of the fuel lines at the header tank as it was put together by the original builder. Each wing tank hose connects to a metal line which both come together at the blue AN tee connector in the center, and the resulting single line (the rubber hose in a loop) goes to the header tank. It seems like some sort of air lock, but how? It's about as simple as a lawn mower, just 2 fuel lines feeding a central header tank. The fuel should just level itself between the 2 tanks. The looped hose seems like a strange configuration, but it really should not make a difference being gravity fed from above and it works fine.

I saw in the online build manual for the Model 7 that the header tank has separate fittings for each wing tank hose, and the vent fitting in the middle. Could the tee connector somehow be causing this problem?

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