1973-1991 Dual fuel tank systems theory of operation

[hatzie]

I'd install the 81-91 Pollack Motorized valve system. The solenoid valves equipped for return lines are made of unobtainium. Nobody makes them.

If you're doing fuel injection get the 87-91 16 gallon TBI tanks with the fuel pump baffles and the in-tank fuel pump & sender. Wire it the same as the 87-91 TBI setup.

The filler neck diameter differs between 73-80 & 81-91 tanks. I've forgotten whether the 73-80 tanks were smaller or larger diameter. They are definitely different.