When I had my engine rebuilt 600 miles ago I set the spark advance according to the recommendations and "tune up specifications for an early 30's Chevy" which I found on this site.
https://1931chevrolet.com/specs7index.htmI made sure the advance was set at 18 degrees. BTC when the engine was not running. Lately I thought the engine seemed too noisy when climbing hills at around 45 mph but quieted down when I pulled the spark retard but lost power, so I purchased a timing light (Innova 3555 Advance Timing Light) and checked the timing with the engine at idle. It turns out that the timing was way too far advanced. I assumed this was due to the distributor automatically advancing the spark when the engine is running. I followed the instructions in the repair manual and using a test light I set the timing at 12 degrees advanced (engine stopped). Then I tested it with the engine running and with the timing light it read 18 degrees advanced at idle. It seems to run quieter on the hills with this setting but may not have quite as much power I'm not sure.
I may be confused reading the VCCA instructions. It says "CONCLUSION: Time it at 12 degrees advanced (noting the mark on the flywheel), with the spark knob pushed all of the way in. After you get the car running, then bump the timing to 18 degrees, and make sure that your AC spark plugs are gapped to .040".
When I set it at 12 degrees when not running It automatically goes to 18 degrees when running.
Has anyone else noticed this? Do you set the timing at 18 degrees with the engine running or when stopped?
At what RPM should the distributor start advancing?