Its entirely possible the fuel itself is causing this problem. I was thinking more about this...when I got the truck out for the first time in early July I filled both tanks. I use the front tank most of the time because the sender in the rear tank doesn't always register accurately. When I first started having problems I was using the front tank, but that tank has since been refilled several times. The rear tank, however, still has the same gas in it from when I originally filled up back in June. I had just switched to that tank on Thursday because I wanted to burn it off before I put it away for the winter. I may have to put more gas in the front tank, drive on the rear one while on the highway, then switch back to the front before I slow down until I get that tank emptied out. Strange though...the last time it stalled the other night I switched back to the front tank before I started it up again but it still stalled as I was pulling into the shed and the carb went dry. Unless the line ahead of that tank was still vapor locked so it was unable to pull fuel from the front tank.

Its definitely fuel related though, not an issue with timing controls. Whenever it quits the carb is always dry. I can crank until the battery is dead after it stalls but If I pour gas down the bowl vent to refill it, it will always start right back up.

 

I had similar problems with my 86 F350 460. Try putting a jumper between the wires on the oil pressure switch on the back of the engine. with it jumper you should be able to hear the fuel pumps run with the ing. switch in the run mode. This could eliminate this switch. also do the same thing with the intra. switch in the cab. I found on mine it was the fusible link at the starter solenoid that operates the fuel relays in the run mode.

 

He has a mechanical pump on the timing case.

Diaphragm pumps don't work too well with vapor, and when they lose their prime it is a long way back to the tank.

 

No electric pumps on mine. This was originally a 351W truck so it doesn't have the hot fuel handling option either. I'm just running a returnless system with a mechanical pump.

 

You might want to see if you can find one of the little vapor separators Ford used, Jim's truck may have one. It goes in the supply line right in front of the carburetor and has a 1/4" return line to the tanks. The only problem would be if you have dual tanks, you would either need a 6 port selector valve, or use two 3 port valves wired in parallel. You will also need to provide a return line into each tank. This will allow a constant flow of fuel keeping the lines cooler.

 

Bill,
I don't have one.
AFAIK they are only in the 'Hot Fuel' trucks to keep the electric pump from deadheading and to keep cool fuel circulating in the lines.

 

I *might* have one of those vapor separators already. Several years ago I stripped down a '85 with a 460 that had been rolled. That truck had the hot fuel package with electric pumps and I still have the engine stored in one of my sheds. I also have two '86 F-250s with 460s and those both have mechanical pumps with a return line on the pump itself instead of the vapor separator. I'm hopeful I can get this worked out without having to re-plumb everything though.

Today it was in the mid 90s so I drove it to work to test things out. About two miles from work I switched from the rear tank back to the front and on the way home I did the same thing. No problems today, so I'm wondering if this whole thing was caused by a bad batch of gas...maybe higher than normal alcohol content since I was running an ethanol blend. Hopefully that's all it was but if it gives me any more problems I'll update this thread.

 

And the problem persists. I always store this truck during the winter and finally got it dug out of the shed last night. I put five gallons of fresh gas in and drove it to work this morning. As I was driving thorough town it stumbled and quit. I left it in gear, let it coast, and it eventually fired and started running again and stayed running until I arrived at work. Tonight after work I stopped and filled it up with straight gas, no ethanol this time. Ran fine going down the highway on the way home from work but shortly after I turned onto my road it stalled again. I was going downhill at the time so I let it coast in gear for several hundred yards but no go. After I finally rolled to a stop I got out, grabbed my bottle of gas I now carry behind the seat, primed the carb and away I went....for another hundred yards until it stalled again. Once again I primed it, drove another hundred yards and it stalled yet again. This time I was within walking distance of my house so I filled a jug with cold water, brought it back and poured it over the fuel pump and lines. After cranking for about 30 seconds it finally fired and stayed running. I let it idle for about ten minutes and it stayed running the whole time.

After last year I blamed it on a bad tank of gas since I was running 10% ethanol at the time and it only seemed to buck on the rear tank. This time I was running pure gasoline and using the front tank but it still vapor locks. I'm beyond frustrated...I'm at the point where I'm afraid to drive it anymore because I don't know if, when, or where it will stall again. I drove this truck for 15 years in all kinds of weather conditions and never had a single issue with it until this suddenly started last year. The only thing I changed before this started happening was the rubber lines between the pump and tanks, and they are routed exactly the same way as before. Adding the hot fuel system is not easily done either since this truck was originally a 351W so it doesn't have any return ports on the senders or switching valve. I just don't understand why it never bothered all those years before. Is it possible the pump is weak enough to allow vapor locks to form? It runs fine going down the highway and never acts like its starved for fuel. The only time this ever happens is when I'm driving slowly, and the problem is often intermittent. Last year I drove it on some 90 degree days without any trouble and today was only around 80.

 

A weak fuel pump might not be liking the hot weather and the ethanol fuel. When I bought my truck the fuel pump on mine was weak, it would keep the truck running fine but it wouldn't have enough output to keep the fuel filter full. Might want to run a test on the pump or just replace it. How old/how many miles are on the fuel pump?

 

The pump was replaced when I restored the truck and rebuilt the engine, around 1998. It has less than 30,000 miles on it. I wasn't running ethanol this time, just pure gas. Last year after it kept happening I blamed it on the ethanol thinking I maybe got a bad tank that was blended too strong and had more than 10%, but it still happens with pure gas.

 

It wouldn't hurt to run a fuel pressure test to see what it's putting out, and how much fuel it's pumping.

 

Just a wild guess... is it possible that the "new" hose composition is such that when it gets to a certain temperature [warm/hot], it softens more than what you replaced and collapses?

 

I'm with David - I think you have a bad hose or a loose connection between a hose and hard line. I had a somewhat similar problem, although I don't know if it was temperature related, and it turned out to be either hoses and/or a bad connection. I don't know for sure as I replaced all the hoses in one go. And I found a loose connection and hose that was so porous that gas dripped through the sides. And it was so sticky that I wadded it up in a ball and it stayed there.

Those two issues have the same result - air gets into the line ahead of the pump and that lowers its vacuum, which is how it moves fuel. So I would examine the hoses, like from the tank to the hard line, hard line to switching valve, etc and replace anything that doesn't look new.

 

Maybe the new hoses are bad and are collapsing on itself?

 

Or have a bad connection.