fuel pump or vapor lock?

1959 CJ5, single-action engine-driven fuel pump (metal cap variety, not glass bowl). Drove it a couple weeks ago, and while I was driving it, it just quit...tried cranking it a while and could tell no fuel was coming through the fuel filter. Took the fuel lines off, blew them out, put'em back on, still didn't work. Took the fuel pump completely apart and put it back together, and then it worked great, jeep started right up after the fuel pumped back through the system.
Drove it only a little since then, and today it quit again while driving it, and again, no fuel coming into the filter.
I originally thought maybe the lines were clogged but that doesn't seem to be the case. Is there a way to check if it's vapor lock that's keeping the fuel from getting pumped? I haven't experienced that before so not sure exactly what's happening with vapor lock. Or is it more likely the pump?

 

Something inside the fuel tank?

 

"Took the fuel pump completely apart and put it back together, and then it worked great."

Specks of crud in the pump's check valves will do that. I like to have a clear glass visible filter just before the pump.

Also be sure the metal dome is sealed well, or you can lose vaccuum.

 

A note about these old tanks. The insides of the tanks have a coating to prevent the tank from rusting. This lining falls off after many years of disuse, and can be a constant cause of plugged fuel line. My tank sat for 20 year dry. The liner looked like flakes to small leaves floating in the tank. A quick way to see if there is rust in the tank is to use a section of magnet (I used one from a refridgerator door gasket) and push it into the fill opening. If you don't have a piece of strip magnet, a magnetic business card refridgerator door advertising magnet, with a hole in it attached to a length of fishing line will let the magent get into the tank. The magnet will pick up particles of loose rust and let you know what you are up against. Today's fuels seem to release coating, making the problem worse.

You can install a T fitting at the input side of the fuel pump and connect it to a vacuum gauge. Since the input side of the pump has to establish vacuum to suck the fuel from the tank, then there should be a vacuum reading on the vacuum gauge. If the fuel line is being plugged by contamination in the tank, which can miraculously disappear when you turn off the engine, a reading of the vacuum gauge with the engine should read rather low, if the fuel is coming from the fuel tank without obstruction. If the vacuum reading is high, then I would suspect that the line is plugged. Of course, if the engine isn't running, then you have to crank the engine to create the vacuum. I took my fuel pump apart and cleaned the rust several times, and even installed an electric fuel pump on the trail to get me home, before I found the detached liner in the tank.

The newer gasoline has a high alcohol content which seems to react with the tank lining, or maybe it is because it is so old.

 

If this is the case, you want to put a filter, either see through or not between the intake side of the pump and the outlet of the tank.

A see-through one will let you see the flakes and stuff the pump is pulling from the tank. And if there is not any fuel in it when the jeep quits, most likely the big flakes have plugged the outlet. Blowing back through the line will clear it.