1968 dual gas tanks, return line empties one into the other!

I have dual gas tanks joined by a tee union closer to the driver tank than the passenger tank. The gas seems to be preferably drawn down from the driver-side tank and partially consumed, with excess being returned to the passenger tank return line. This is resulting in my driver tank being emptied, with air eventually being introduced into the system and both tank lines losing their prime. The passenger tank with the fuel sender ends up holding more gas at the end of all this than it started out with and virtually none in the driver side tank, and no gas to the engine! I blew 120 PSI into the tank Tee and both tanks bubbled well, so the lines are clear in one direction at least. I am perplexed about this behavior and considering only using the passenger tank with the fuel sender and isolating the driver side tank. Any help on ideas is welcome.
John

[DTW1086@cox.net]

I had this problem one time back when I was driving gas power BlueBird Schoolies in the 1960's. Problem was someone had changed a gas cap. Had one vented cap and one non vented cap. Get 2 vented caps on it and the problem should go away.

[78bbird]

My 1969 Blue Bird INN has 3 gas tanks and a manual switch next to the shafter, I would turn from tank to tank as I empty them. It is a three way fuel valve.

Originally Posted by DTW1086@cox.net

I had this problem one time back when I was driving gas power BlueBird Schoolies in the 1960's. Problem was someone had changed a gas cap. Had one vented cap and one non vented cap. Get 2 vented caps on it and the problem should go away.

Wow, I should be so fortunate as it be so simple! I'll go transfer some several gallons of gas from the passenger tank to the driver tank and keep both of the gas caps loose and hope for goodness! Thanks for the idea to try . Otherwise, it looks like I'll consider installing an electric fuel valve with switch on the dash and make the fuel sender tank the default.
John

[GregOConnor]

the returns should blow clear and the equalizer between the tanks also. On a diesel there is usuly a backflow device in or near the pickup that would keep air clean out procedure like you describe from blowing bubbles in the tank. diesel 3208 and the 8v92 return a bunch of fuel to the tank as the diesel disipates heat from the injectors and is used to cool engine computers in my cummins n14. put you hand on the tank of a big rig that is pulled up for refueling and notice the warm temp.

[mk199]

Originally Posted by 78bbird

My 1969 Blue Bird INN has 3 gas tanks and a manual switch next to the shafter, I would turn from tank to tank as I empty them. It is a three way fuel valve.

Mine is the same.

While I have passed the 68 Bluebird on to a new owner, I figured out what is happening: The gas line from the driver side is clear, the gas line from the passenger side is not. When I start the bus, it draws gas from the driver side tank, and dumps the excess not used by the carb back down the return line to the passenger tank (which is not sending gas due to blockage). Quickly, the driver side runs out of gas and then draws air from the driver tank. I know the air is from the driver tank because I put in a one-way valve in the return line to prevent this if that was the issue on that line. Once this situation developed I measured the gas level in the passenger tank and it was higher than when I started the engine by a considerable amount! There is no equalization line between the two tanks or this would have never been noticed at all. I put a fuel line hose into the passenger tank and connected to the fuel line right on the carb and that worked as expected. The conclusion is the line from the passenger tank becomes blocked by rust and sediment even though it blows out fine, it quickly re-blocks. The new owner will have to pull the tank and clean it.