Mechanical advance spring.

1994redram said

This distributor was set at 6-8 degrees idle and was at 35 all in. I'm hoping to bring the base timing up to 18 or so and see how it acts. Unfortunately, I didn't pay any attention to WHEN the advance happens.

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You need to find your initial timing happy place and then limit the mechanical advance to 34-35° by welding up the slots or using a advance plate. Then you can mess with the advance springs. Like mentioned, taking out the heavy spring and replacing it with a factory light spring or a Mr Gasket spring. Too light of a spring will advance too quick and cause ping.