I have been having problems getting my 1978 F250 to run right. I just changed the timing chain, fuel pump, intake, carb, and put in a 38-gal. fuel tank. The trcuk would start, but wold only run for a littel while before stalling out. It would not restart unless I let it sit for a while, then it would start, but would eventually stall out. I even put the old carb back on to see if that was the issue, but it didn't change.



OK, so trying to isolate the fuel issue. When truck sits overnight, or for a couple of hours, it will start, but will only idle for a short time and then stall out. You can see the fuel filter go empty. This is what I did today:

• I disconnected fuel line from carb and spun motor. Very little fuel came out. To see if this was s fuel pump issue…
• I disconnect fuel pump inlet line and inserted it into a jar of gasoline. Truck started right up and I watched it idle fine as it sucked all of the gas out of the little jar. (picture 1)
• To see if there was a clog in the line between the pump and the tank, I tried to siphon gas out, from line down near tank, but got nothing.
• I looked at the tank and I noticed a dent on the bottom side, as if it had been sucked in (picture 2). I just put this tank in two weeks ago and I know I didn’t dent it. Is it possible that something is causing the tank to collapse, but not get any fuel? This is a new 38-gal tank and I did have to extend the pickup. Might that have been inserted wrong, or perhaps the pickup weld came apart?
• I figured I better siphon the gas out of the tank just in case I had to drop the tank and I noticed that when I was pulling off the filler hose, quite a bit of fuel leaked out, which surprised me considering this tank couldn’t been more than ¼ full (picture3 ).
• Just to try something, I inserted the fuel line in a 5-gal jug back near the tank, and the truck ran fine (picture 5).

I think I know the answer to this, but do I have to drop this tank? Might this be some kind of vent problem? I thought the tank install was pretty straight forward, other than extending the pickup line. Plus it would run for a little while, before stalling out, Any recommendations to try, or should I just drop the tank? Even with 10+ gallons of fuel in the tank, my gas gauge really didn’t move. It worked fine in old tank, and it does have a good ground.

Thanks,
Frank

 

So i dropped the tank. I noticed that where the fuel line attaches to sending unit, it may have been a little kinked, but not sure it was enough to starve the truck.

Does the orientaion of the fuel senfing unit look right in the first picture?

Should I remove it to see if the tube that was weleed on fell off? If I do, will I need a new gasket to re-install? This gasket is literally two weeks old.

I attached the fuel line with the tank on the ground and the truck started and ran fine (pic 2).

 

When you had the tank on the ground and testing it (last picture), was the gas cap on it? If not, then I would think you need a new one, and make sure it is the vented kind. Judging from the earlier picture (of the tank bottom), I would think your cap has gone bad, and since there doesn't appear to be any other vent on the tank, the cap is the only place for it to get air.
As for your gauge, if you extended the pickup tube, but did nothing to change the location of the sender unit on the tube, it will not read anything until you put enough gas in it to "float the bobber". In that case, when it is full, the gauge will read full, but when the gauge reads empty, you will still have almost a half of a tank of gas left.

 

Agree with drumfield...everything points to a non-vented gas cap.

 

Thanks. I re-installed the tank and made sure the kink was out of the hose at the sending unit spout. That seemed to do the trick. It started and I drove it around the block a dozen times and it didn't stall. I also noticed that the see-through filter near the carb remained half-full.

I was not the one who extended the pickup tube, but even after putting $40 of gas in it (about 12 gal) the gas gauge did not move. I am going to fill it up tomorrow and see if I get any reading on the gauge.