I have a 1972 Fiat 124 Spider that I’ve been in the process of doing a poor man’s restoration of; starting in high school and resuming now in my thirties. Everything seems to be working fine (relative to a 72 fiat) except the fuel system (minor issue). She starts and runs great cold but just stops pumping fuel when warm. I have replaced the fuel hose, rebuilt the carb, and replaced the diaphram in the fuel pump. I have no idea what to do to solve this issue. Guessing I screwed something up here, but what?!
-I do have a crack in the header pipe and a small gas leak in the accelerator control arm of the carberator that the rebuild couldn’t fix. And a leak along the seam of the gas tank (can I use JB Weld as a quick fix for this?). Many thanks for help! 
I have to believe you when you say it stops pumping fuel when warm, so I have to think why would it stop pumping fuel when warm. I don’t think the pump is the problem, so my initial thoughts lean to sediment clogging up the carb, or fuel filter. Was this car equipped with a sediment pick up sock in the tank?
The reason I say it quits pumping fuel is because I replaced my new metal fuel filter with a clear plastic one as a diagnosis tool. The filter is located between the fuel pump and the carb. It literally pumps a little fuel going to none once it warms up. The fuel tank was filled with a ton of sediment, which I cleaned out to the best of my ability (removed the tank and shook it all out then rinsed with gas). I replaced the filter in the tank with one I made, but the same design. It’s a cut up metal coffee filter fastened to the end of the fuel line. I cleaned the metal fuel line between the tank and the fire wall with Sea Foam by injecting a half a bottle, letting it sit, and then blowing it out. Seems clear. I’ve been wondering about the fuel pump. I bought a new one, but the control arm was too different to work (the same “fiat” specialist has had my head pipe on back-order for 4 months), so I used it’s diaphram in the old one. Could a poor seal cause vapor lock or some other thing?
If the pump works when things are cold, then the pump works. Does the engine stall when it warms up? Sometimes the fuel filter just does not fill up, but things work anyway. Is there gas in the float bowl when this situation happens? Is this a situation where the sediment is blocking the line somehow and it falls back out of the way when the suction is released? Clearly I’m just guessing. Another thought is that the gas tank vent system is plugged, so the fuel pump is pulling against a vacuum, but that seems unlikely.
OK, I just went and fired her up to check the float bowl. It barely would run, choke, no choke. I also got a few “pops” with smoke out of the carb. There was gas in the float bowl. I opened the idle all the way up, and still just chug, chug. The spark plugs show rich fuel mix. Argh! My problem had been consistent (for a dozen or so go’s) until today. Is this all a carb issue?! A 400 dollar carb is not in my budget, I need a paint job and a 16 foot Hobie Cat (another potential mental illness)!
If it is popping through the carb, then it sounds like a timing problem. To your knowledge,ha the timing belt been replaced. If my nightmares of those engines serves me well, that belt had to be replaced every 25,000 miles. Uncover it, but if you have not toyed with it before don’t do it now, just look it over.
Oh dear god. I replaced the engine in high school, and my best friend’s Dad (a mechanic) gave me a timing belt as a present saying “you’ll need this sooner than you think.” It ran great for a few thousand miles before college (and a bizillian other problems, mostly now fixed) required a hiatus. Could it somehow have gotten out of timing in storage?
OK, did a quick visual inspection of the belt, without removing the cover. That requires draining the cooling system, if I remember, which I don’t feel like doing right now. It looks OK. The tension is good, the belt teeth and all seem good. She “popped” out of the carb again after breaking while in gear at about 4000 rpm-- going for a quick spin in the horse pasture. It then died but restarted right off. I didn’t get up to full operating temp, so I can’t say about my original no gas seeming issue.