I have a 1995 Nissan Sentra with a carburetor and a mechanical fuel pump. After being parked for a couple of days, the car doesn't start because no fuel reaches the carburetor. At most it, will start and then die after about 30 seconds, when the fuel that was already in the carburetor runs out.
I called a mechanic. After checking things a bit, he disconnected the fuel line from the carburetor, sucked from it (literally, with his mouth) until fuel came out, then plugged it back in. The car then started and ran fine for at least 15 minutes, including at high RPM. It restarted several times without a problem, too. It takes a couple of days of being parked for the problem to reappear. The mechanic said that there's probably some valve broken inside the fuel pump which causes it to be emptied of fuel after being stopped for a while, and then it can't pump fuel anymore unless it is "primed" like he did by sucking. Therefore, the fuel pump needs replacing.
I've been researching online, but I haven't been able to find descriptions of similar problems. From what I gather, the fuel pump either works or it doesn't, and if it's "sort of" failing, it's most noticeable at high RPM, not when starting. And it seems that fuel pumps don't need priming.
Does his diagnosis sound right? What else could it be?