O.K. here is the situation with my daily driver 48 coupe and what I have done so far.
About 3 months ago I thought I had run out of gas (guage does not work) so I added some gas from the 2 gallon can I carry in the trunk and made it to the station. A couple of weeks later, ran out of gas again only this time I knew I had gas in the tank as I had just filled it the day before. So, I let it sit for about 4-5 minutes fired up and ran several miles then like it ran out of gas again. Same thing let it set a few minutes fire it up and go only the distance traveled got shorter each time. No swoosh when the cap is removed so I think I am getting good venting of the tank.
Changed the carb, dropped/cleaned the tank (a lot of crud in there) blew air back through in tank filter and ran it a few days no problem. Then it started happening again. Changed fuel pumps from spare engine and it ran fine for about 2 1/2 months. Then Friday it starts all over again. Took me about an hour to get back home a total of about 4 miles. Bought a new NAPA fuel pump and it ran fine Saturday until this morning. Made it about 2 miles from home and it started again. Since I was dressed for work and now late for an appointment couldn't crawl under to see if there was fuel in the bowl.
It acts like it is running out of gas. Runs fine then starts sputtering and then dies. Let it set, try to start and the engine cranks over several times then starts runs a little rough then smooths out for a few blocks then happens again. If I keep my speed down it runs longer. Which makes me think that the higher RPM empties the carb bowl faster like the pump is not keeping up then the engine cranking fills the bowl for the next short run period.
Anyone have any ideas? Could it be the coil going bad and as it heats up gets intermittent spark? Sorry for the long winded explanation but I don't know where to look next.