HARD start when warm

It is a 318 with electronic ignition. It starts great when cold, but after I drive it a bit, it is very hard to start. Did a tun up last summer, and that seemed to help. The car sit all winter into early spring. Brought it home last Monday, and everything seemed fine. But it atarted doing it again, thought maybe the $20 carb i put on it was the problem, went out and bought a new one. Fired right up once gas got into the carb, ran it for a bit, shut it off. let it sit for a few minutes, it started right up with out hitting the gas, took it for a drive, got home. shut it off and let it sit for a few minutes, tried to start it, again it didnt start. let it sit for a couple of hrs, started right up.