So I've got a 1979 f250 with a 400m that I just replaced the fuel pump on. It ran and drove great around the farm for about a week, but I needed to fill it up with gas. So I drove it to the gas station in the ditch because it's not registered yet. It died on me twice on the way there, and as soon as I filled it up, I couldn't get it to re start at the gas station. I let it sit and it started and I got it a little way down the ditch before it did the same thing 4 more times, and finally wouldn't re start and had to tow it home. Any ideas why it's doing this?

 

Since you were into the pump,,

When it "doesn't start", take the air cleaner top off, and pump the throttle linkage (ignition off) while looking into the carb throat. Do you see the accelerator pump spraying steady fuel streams at the Venturi during throttle extension? If so, then check for an active and hot spark with either a grounded extra spark plug, or spark tester, or spark plug wire end terminal held 3/8-1/2 from a good grounding location. Coil wire first, "check, ok HOT", then out to a plug wire. Helps eliminate cap/rotor shorting issues that way.

One of the other things that was common, was the 'power valve' under the fuel bowl would leak with age and internally into the intake manifold (sometimes causing a flooded condition after some sit time) and make for a hard restart unless you cleared the flood with the throttle. If leaking is more severe, it would create a rich condition, but you said it was running fine prior. Just something to consider and look out for with the old iron.

Also, if a NO or intermittent spark, the ignition module or the distributor mounted pick up coil may be cause or suspect. Generally if it stalls, and is allowed to cool, sometimes a restart. Most will be intermittent prior to a full on failure. Checking for spark immediately after a stall can help point to module/PU coil failures..