I have recently bought a 85 F-250 4x4, with the carburated 460. It has dual fuel tanks, and I am only using the front. For some reason, the rear won't "take" fuel, it just spits it out 'as soon as' tou try to put it in. The tank switch seems to work, it goes to the rear and the guage starts to drop to empty. Also, the other day, when I took the rear cap off, stale gas sprayed out. There are also two different steel lines running up to the motor, one is hooked up to the carb as a feed, the other is open (not hooked to anything) right now as someone has been under the hood doing who knows?? Is this second line a return, or are there two feeds? And if so, how did they hook up? Any insight as to how to make the rear tank work, and what to do with this other line???

 

Easy way to tell is to look at the tank selector valve and see if it has 6 ports. If it does, and the "free end" goes into it, then it definately is a return valve.

The tank selector valve is on theinside of the drivers side frame rail about mid-truck.

As for gas, you can always try to siphon out the contents. If something comes out it's full, if not it's empty .

There was a thread on trucks that have problems with the fuel pump at the gas station shutting off even though the tank wasn't full. Easy solution was to fill it up really slowly, I think the real reason was something shifting in the filler tube. You may want to search for that article if you continue to have problems after you verify your tank is empty.

 

Here's an old thread on a f250 with a 460.

https://www.ford-trucks.com/forums/s...=f250+AND+fuel

It had a "hot fuel handling" type system with electric fuel pumps in each tank, and a vapor seperator on the fuel line to the carb, which also hooked to a fuel return line to the tanks.

I would also go ahead and take the fuel filler neck off the tank and investigate if it has a blockage, or the little pipe inside has come loose.