I have an '80 F-150, 4WD with Straight 6, manual transm., with dual fuel tanks. When I switch from main tank to aux tank, after 10 to 15 seconds the engine stalls like it is not getting gas. I just replaced the fuel selector valve, and this did not fix the problem. When removing the old valve, gas came out of both lines, so it appears they are not clogged, and both tanks have gas. Can anyone offer ideas as to the problem?

Does this truck have electric fuel pumps?

I'm not sure, but I can tell you that it only has one fuel pump. The set up has a tank selector valve that is located between the tanks and the fuel pump. Each tank has a line coming in, with a single line going out to the pump and then on to the carb. I have replaced the selector valve, but still have the problem. I am going to try and place a piece of clear tubing between the rear tank and the selector valve to see if gas is flowing when I switch it over. If it is, then I believe I may have water in the gas, at which time I'll treat the gas or drain the tank. If there is no flow, the I'll have to look for another problem.