Have you tried connecting the vacuum gauge to the line you disconnected from the distributor? That's the simplest way to see if there's any vacuum on the distributor at idle. Ideally, there should be virtually nothing there until the speed is raised a little, then it should increase gradually as the RPM goes up. Just as a precaution, even on engines that supposedly idle with no vac advance, I disconnect and plug the distributor line BEFORE setting the timing. Then I recheck the timing marks with a light after locking everything down and reconnecting the vacuum.
On a long hill or during passing, etc. the vacuum advance goes away and the engine only has whatever timing advance the centrifugal weights are providing. The only reason to have vacuum advance at all is for light throttle cruise, to improve fuel economy. Anytime the engine is under any load at all, vacuum advance will be nonexistent.
Jerry
