Vacuum advance issue

Next thing I would do is map out the vac advance. Use a vacuum pump and your timing light. Connect the pump to your advance canister and add vacuum 1” at a time and check the timing just to see what it’s doing.

Probably wouldn’t hurt to map the mechanical advance by rpm also. Say @500-1000rpm increments w/o vac advance. Never hurts to know exactly what’s happening and when.