[olddog]

The gauge should be reading inches of mercury for vacuum. If it is reading psi or psig your most likely reading pressure. Are you sure you are pulling vacuum? You can put a finger on the hose to tell.

An engine would pull more like 19 inches of mercury ("Hg or in-Hg) at idle, unless the cam has a lot of overlap in the valve timing. You may not be pulling enough vacuum for it to move.