Mallory Hyfire Ignition problem

68Valiant225 said
It's a 690 part # branded as Mallory.

My coil is mounted on the intake, I'm kinda wondering if the heat is the problem. What coil are you running?

It's a Mallory race only coil on my Dart Sport race car. Not a good idea to use one on a car seeing extended driving.

Not particularly specific: https://static.summitracing.com/global/images/instructions/MAA-690.pdf

As for something overheating & opening the circuit, it could be coil or something inside the box.