Fluctuating neg. to ground on ignition coil

Stephan D said

After reaching operating temperature AND being shut off for 10-30 minuter the idle is just perfect, if it run like this all the time I would be VERY happy:

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I had a Ford 302 act just like that. It would start to run rough and miss erratically when hot. If I stopped at a store for 5 minutes and started it back up, it would be perfectly smooth. I replaced the intake manifold and carb base gaskets, thinking that it had an erratic vacuum leak, related to temperature, but that did not fix it. I never found the cause; I worked on the ignition system, replacing a lot of the parts, and that intake manifold area. I cannot recall if enriching the mixture made it better or not. I never replaced the carb or the distributor or coil.

I sold the car as-is for $600, and the buyer drove it as a daily driver like that until he junked it.

Honestly, with the compression readings and the smooth operation you see at some temps, then I do not think there is anything wrong with the cam. I suspect fuel-air mix or ignition.

One thing to think about is that if the engine sits for 10-15 minutes, the temperature is going to go up as the coolant is not circulating. That might effect the vaporization of the fuel.... just another guess of what might happen!