Reply to "spark timing"

This is one time when a Chevy would be ideal?

The mechanical advance is not returning to rest inside the distributor.

Weak, disconnected or stretched out advance springs will do that. It is very common in aftermarket distributors because they install light tension springs in them new, unlike the Ford distributors which have much heavier springs.

By contrast, Ford distributors would be all in around 5,000 rpm instead of 2,500 rpm, so the tension on those springs is about double what the aftermarket supplies.

My Mallory distributor as well as my Accell had what I would call "drag race" advance springs in them. That's the way they came new.

I went through this issue here when we lost leaded 103 octane gas in the pumps around 1975.

The Ford unit can be tuned to come all in 2500 to 2800 using one heavy spring and one light spring but the issue really is the quality of the metal used in the springs.

Ford's are very high durability while aftermarket sources them from "offshore". That target keeps moving. I suppose it's so that you can't use a killer satellite and zap them with a laser from space?