@Ward57, the way a vacuum advance works is this way,
No vacuum is needed at idle.
The mechanical weights below the breaker plate advance timing with the greater rpm(until you reach max advance)
So say you're at a stoplight and nail it, this is where the vacuum advance takes over. The ported vacuum on the
carb increase vacuum as the rpm rises. This in turn pulls the breaker plate to advance timing much faster than the mechanical weights. The result is more power off the line.
This is why you don't run off manifold vacuum. You would have full advance at idle and timing would retard under heavy throttle, until the mechanical advance could catch up.