If you disconnect the vacuum line at the distributor and attach a vacuum gauge to the line, the vacuum should build up gradually as the engine speed is increased- - - -little or no gauge reading at idle, and almost equal to full manifold vacuum at around 1500 RPM or more. If that works, chances are there's a hole in the rubber diaphragm of the advance unit. The old scool method of checiikg one was to blow cigarette smoke into the fitting and see of it comes out on the linkage side, Now it's probably better to use a hand held "Mityvac" pump adapted to the vacuum chamber with a short piece of fkared tubing.
Jerry
