Your coil could be the culprit
My 1956 Chevrolet Bel Air, which has its original 265 V-8 in it, is giving me fits. It starts fine and idles smoothly, but after I have been driving for a few minutes…it cuts out. It sometimes kicks back in and goes on running, but other times I have to pull over and restart it. It also backfires on occasion, and it seems to be running hotter than usual, though not overheating.
I thought there was possibly air in the fuel lines or a blockage, so I blew out the fuel lines, checked the fuel pump, and checked the needle valve and float level on the carburetor. Everything seemed right. I also checked the points, rotor, condenser and distributor cap and they are all reasonably new or in good condition. The sparkplug wires are new too. What have I missed?
It sounds like you have a failing coil. It is possible that you had the ignition on too long while the engine was not running, which can make the coil get hot and cook itself, or it is possible that it is just old and on its way out. Take it off and shake it. If it rattles, it needs replacing. You also can check a coil with a multi-meter if you have one, or you can just attach another coil and see if it solves the problem.
When you purchase a new coil, don’t be tempted to buy some super-hot performance model. Just get the correctly rated one for your car and make sure it does not have a ballast resistor built in. The expensive, hot-performance coils are for an HEI ignition, and will not work well for your application. Also, you don’t need a ballast resistor, because your car already has one up on the firewall right from the factory.