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My '47 has an electric fuel pump. It's been in there a lot of years already. Several times lately it has been known to lose its prime after the truck has sat a while. It doesn't always do it. It might sit for several weeks and then start right up, but the next time after only a couple weeks the truck will not start till I pour some gas down the carburetor. All the connections in the fuel line and around the pump are tight and it doesn't seem to be leaking anywhere.
I guess my questions are--why would this be happening? The pump IS quite a few years old already, but the truck does not get driven that much. Could it just be wearing out?
Second, why would pouring gas down the carb make it start working again? Seems that if the pump wasn't working, then it shouldn't work at all. I've tried leaving the key turned on for a few seconds before cranking it, thinking that it would give the pump time to catch up, but that doesn't make any difference. What am I missing here?

Easy to check, just disconnect fuel line at carb and turn switch on. If it pumps out gas the pump is good and it's something else.

Hi Rich,
It is located back by the fuel tank, yes? Do you know what make it is? It could be wearing out, but it also could be that something is blocking the fuel line somewhere. If you have rubber hose connections (common on electric pumps installed in the line from the tank leading up to the engine), I think I might look there first. Usually those hoses will deteriorate from the inside first.

In the late 60's when I was In my early 20's I purchased a 53 1/2 ton with an electric fuel pump mounted on the fender well. One day it quit running due to fuel starvation. Checking it I discovered it had a built in fuel filter that was completely blocked with trash.

The old Bendix type solenoid pumps had a removable bottom cap with a filter under it. They were noisy, and had a bad habit of overriding the needle valve in the carburetor(s) and pumping the engine full of gas if it stalled or the pump was left on by mistake. The newer style rotary pumps that resemble a metal fuel filter with a couple of wires attached are quiet, provide plenty of volume for most applications, and don't overpressure as badly as the older style pumps. It's still a good idea to put an oil pressure switch and a relay inline with the pump, with a momentary contact push button for priming purposes.
Jerry

You described that old fuel of mine near perfectly except I had very few problems with over fueling.

Are you giving the fuel pump time to refill the carb bowl after the gas has evaporated out of it? My fire truck was that way...run the pump for about 10-15 seconds and you could hear the pressure build up, then hit the starter and it would fire right up.

Mike B

As you say, priming the carb does not make the pump operate better. In a way it does, because of what Mike B. said. The extra time the pump needs to get fuel into the carb bowl is obtained by you prime starting the motor and it running separate from the pump. The pump "catches up" but it seems like the carb prime had an effect on pump pressure. Letting pump run longer before starting will prove this theorem.
FI motors have this pressure-up feature built-in.
You may also have a weak pump due to age or blockage. Probably time to replace. Make sure it is a 3.5-4 max psi pump.

Even's test is the next thing to do. You can even time it. Do this test after it has been sitting.

The only thing I can think of for why it does it only sometimes is the weather. I.E. evaporation rate of bowl gas.

It is slightly possible you have a intermittent venting problem. This could be weather related also. I.E. barometric pressure.

How did I get on this weather kick? I don't know where all that is coming from? The weather I guess.

Thanks for all the input, guys! A number of good things to check out here. So far I have not done any troubleshooting on it, as this usually happens when I'm in a hurry to move the truck or take it someplace. Hopefully I'll be able to dig deeper into it if/when it happens again.

My pump is the small round type that looks like a metal fuel filter. It is mounted back near the tank and has another metal filter inline between the tank and the pump. As Jerry mentioned, it is very quiet. I assume the filter is not plugged, as the truck runs fine once I get it started. I think the carb is due for a rebuild though, as the accelerator pump is not working the way it should.

I will try giving the pump a bit longer to catch up and see if that makes a difference. Not sure how long I waited last time--maybe it was only a few seconds, although it SEEMED longer than that. Maybe in reality it wasn't.

Thanks again for all the suggestions!