what causes this to happen

I think maybe your fuel is going back to the tank. Wait till the car is completely cool, then pull the coil wire. Crank the car for a bit, then see if the accelerater pump squirts fuel. If not, crank it some more for 5 or six seconds at a time to keep the starter cool. After the accelerator begins to shoot fuel, crank it a couple seconds more to be sure the carb is full. Put the coil wire back on, replace the air cleaner, and close the hood. Let it sit for a few days, then go out and try to start it. If heat was your only problem it should start fairly easy. I drove my 440 for years up north with no choke at all. Pump it two or three times if real cold, hit the key and it would run.