There should be a ported vacuum nipple that has little or no vacuum at idle, and gradually increases as the throttle opens. The initial timing usually works best at 8 to 12 degrees, with the centrifugal advance coming up to 35-37 degrees (including initial) at around 2500 RPM. At light-throttle cruise with ported vacuum on the advance, 40 to 45 degrees (initial, centrifugal, and vacuum combined) isn't excessive. The vacuum advance will drop off very quickly when the throttle is opened during acceleration.

On the centrifugal-only race engines, best horsepower usually happens around 36-37 degrees. The extra advance a vacuum unit provides is strictly for light-throttle cruise fuel economy.
Jerry

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