[Tom Endy]

I suspect that the high voltage windings in the coil are shorting out at high temperature. When you stop after driving the temperature under the hood goes up and the heat causes the windings to expand and if some are bare they can short out.

I had the same thing happen to me a number of years ago on a trip from L.A. to Yellow Stone. I had just installed a new high performance coil (6-volt system). When I stopped for gas north of Las Vegas the ambient temperature was 104. After I gassed up the car was difficult to start. it coughed and sputtered for he next few miles, then began running ok. Every time i stopped for gas it was the same drill. When we got to Yellow Stone it was cold there and for the next few days the car ran ok. On the way home down through hot country, same drill.

A few days after I got home the car would not start. I put the original coil back on and the car ran fine. I sent the coil back to the high performance dealer, he sent it back to the high performance manufacturer and they tested it and reported there was nothing wrong with it. I asked if they tested it with a temperature cycle. They had not. I threw the high performance coil in the trash. A Model A does not need a high performance coil.

Tom Endy