Also, FWIW, I've noticed that the original glass-topped fuel pump works a heck of a lot better than the modern all-metal replacements. The modern ones would deliver fuel, sure, but they didn't seem to deliver enough and I had the same issues you describe. I ended up adjusting the mixture so that it would run right, but I had all kinds chugging when the truck went up a hill, and problems starting the engine.
And this was after I had rebuilt and cleaned up the carburetor and had the tank cleaned up, and replaced the fuel filter.
I finally compared the rebuilt pump to the replacement I'd purchased, and it was no contest. While the modern metal unit did deliver fuel up through the fuel filter and to where I'd pulled the line from the carb, the stream wasn't terribly strong.
The glass-top unit almost hit the firewall.
The old girl runs a lot better with the old rebuilt unit. Dunno why the new ones don't seem to be as good.
