Fuel starvation

Greetings All!

I have a 1949 KB-5 that is all original with a Green Diamond engine. It was running fine but now won't stay running. I can pour some gas down the carb and it will fire, then quit. The fuel pump output line was removed from the carb and the engine turned over. The pump was not pushing any gas. I put five gallons in the tank. The pump was still not pumping. I pulled the metal screen out of the bottom of the pump (mine does not have a glass bowl). The bowl in the bottom of the pump was dry. I pulled the fuel inlet line off of the pump and blew air backwards toward the fuel tank just in case the pickup line was blocked. I then put a small amount of pressure in the tank and could see gas coming out of the pump inlet line from the tank. The truck then started and ran for a few minutes before it died again. I can put mild pressure in the tank for a few seconds and get the truck started again but it will soon die. My question is "Does the fuel pump not have enough suction to draw from the tank or is there a blockage in the tank (screen on the pickup line?)?

If it is the pump are they easily rebuildable?

My thanks in advance.

Most older pumps are rebuildable. A real common problem is the suction line from the tank to the pump gets pin holes in it, no gas leaks out but air leaks in. If that line is not new, it might be time to change.
There are fuel pump suction/pressure gauges to check the operation of the pump.
There are places like Then and Now in Weymouth, MA that will do a good job rebuilding you pump. You can do it yourself, but by the time you get a "kit" and learn how to do it without damaging fragile casings, You likely be miles ahead having them do it, I was happy with the one they did for me.

Then and Now Automotive in Weymouth Massachusetts has the kits or You can send the fuel pump to them and they will rebuild it.

https://www.skf.com/mityvac/products/ha ... hand-pumps

This is a very handy tool for diagnosing fuel line leaks. I bought the vacuum only unit 25 years ago, then 7 years later I bought the convertible vacuum or pressure model.
The uses for this tool go far beyond testing fuel lines.
Amazon sell MytiVac by Silverline.
Back a few years ago, when I was still driving my R120 Diesel, the truck was plagued with a difficult re-start situation after being parked for more than 10 minutes. The Diesel shop who rebuilt and installed the fuel-injection pump was unable to find the problem. On the suggestion of my supervisor, I bought a MITYVAC and found a leak back to the tank situation. A simple in-line check valve fixed the problem.

Thanks to all for replying. I suffer from low pump pressure. In my opinion either: 1. The fuel pump needs rebuilt 2. The draw line from the tank will suck air, or 3. The cam lobe is smoothed off and not cycling the pump. I can cycle the pump by hand and it will spit gas at me but that doesn't mean it can do so under pressure. Given the age of the pump I have decided to send it to Then and Now and have it professionally rebuilt and start there. I feel that is the most likely issue. That will cost about the same as buying a 6V electric fuel pump but save me a lot of work trying to get the lines to match the pump and wiring in a switch.

Thanks to all for the input.

fuel lines can be half clogged from rust or fossilized gas, my KB-6 line let some fuel thru but it was full of prehistoric gas molasses,

was nasty stuff, couldn't get it cleaned, replaced it,