Hello fte! I'm new here and I'm about to pull my hair out trying to solve a tricky issue.
I have a 1985 f-250 with the dual tanks, 460 motor, 4 speed manual trans, electric pump on driver side frame, and the 6 port selector valve with the switch in the climate control cluster on the dash.
Her name is Sally and she is my beloved
A couple weeks ago she was working perfectly after installation of a new 750cfm edelbrock carb, new cap/rotor, new valve covers and gaskets (edelbrock sig series), etc.
Out of nowhere she began to bog down at around 50mph and at the same time the fuel selector switch stopped working. She is stuck on the rear tank.
I visually inspected the underside and engine compartment for any damage etc but everything looks fine. No broken wires, no obvious damage to the fuel tank selector valve which is also mounted on the drivers side frame just behind the electric pump and the pump is still functioning. I can get her to start without much difficulty but when I get her on the highway and up to 50 or more she bogs down. I can't switch the tanks to front because the switch isn't working.
I have no idea what to do to trouble shoot this nor repair it. I could use some help.
All filters have been checked, replaced, all lines have been inspected for holes, wear, all electrical connections have been checked, carb has been checked and rechecked, I am at a complete loss.
I was told to check the fuel tank selector valve and I ordered one off ebay (6 port) but it turns out that valve assembly has the 4 port side facing the wrong way. I'd rather not twist my fuel lines around to make it work and finding the oem for this year has been challenging to say the least.
I am new to this forum and I could use some help here. Thank you all for your patience with me

 

The original valves are hard to get and very expensive when you do find them(I want to say in the $200 neighborhood). So if you find you do need a valve, I would go ahead and modify the system to take the valve the parts stores sell, and then later on the same valve will fit. They are made by the same company by the way(Pollack).

The 460's are like the diesels, they have a large plastic pickup piece in the tank people call the "shower head". These plastic showers heads can break off, or they can disintegrate. When they break off, you have to keep at least a 1/4 tank of fuel or you run out. When they disintegrate, little plastic particles get up into the fuel system and cause trouble.

I think you also need to pull the tanks to look at what's going on inside. The pump on the frame rail is not original. You originally had a pump in each tank. Whoever added that pump, did they take the old pumps out of the tanks? Or are you trying to pull fuel through the old pumps?

 

Well, thats a great question lol, I have the forward tank full of fuel and the rear tank is half full. I guess Im gonna have to figure out how to drain and store all that fuel before I can drop the tanks and look inside, unless you know of a way to get in them without draining them? (sounds explosively dangerous to me lol) As far as I know they (the tanks) are unmodified but I will have to verify that.
As for adapting the new valve style to the truck, won't the bends required to make the connections stifle my flow?

 

I have a second f250 with dual tanks I could move the fuel to but it has a hole in the rear tank as well, hmmmm tricky no?

 

Check the fuse that controls the valve switch. I fought mine for a few days and realized the fuse was blown. That was all it was. Valve itself was fine.

 

I would ask Bill K, aka 'Subford' for the diagram.
He has moved or deleted it from his Photobucket.

I know it differs from the 1986 wiring... and I don't have the EVTM for '85.
IIRC the dash switch controls a relay, that in turn controls the switchvalve.

FYI,
Electric pumps work much better pushing than sucking, and the Pollak valves are meant to operate that way.

 

There was one guy on here with that problem, and I believe he just mounted the valve in a different position. I believe also some just use on bolt hole and mount it in the different position.

Actually the tank is more explosive with less fuel in it, but you are correct, you need to get that fuel out, it's very heavy and even with most of it out, it will still be heavy and want to slosh back and forth and makes it hard to handle. I use a floor jack and another person to operate the jack while I steady the tank.

Some people lift the bed up off the truck to do tank work, but that presents it's own headaches, with rusted up bed bolts.