If the vacuum reading point were closer to an intake valve than a more central location, could it be reading instantaneous changes in vacuum as that valve opened or closed?

John - "The Hoosier Hurricane"

Robi’s suggestion to run a compression check on all the cylinders is a good one.  That test by itself can either isolate the problem or rule out a majority of possibilities.  Beyond that, the irregularity of the vacuum reading could be as simple as readjusting the valves or as complicated as a worn distributor shaft causing excessive runout at the points.

Lorena, Texas (South of Waco)

idle it is between 11 to 14. overlap shows 48 deg on the cam card. It flickers at all rpms.

Kenny  Onalaska, Texas

How much does it vary in inchs of vacuum?Does it appear to be random or at regular intervals?

  

It would have to be a fairly big cam with a lot of overlap to cause poor vacuum.  Most likely you have a leaking or a burned valve.  I would suggest a compression test and a cylinder leakage test.  If it is a leaky or burned valve the leakage test will find which one it is.  It is also possible that could have a cam lobe run off.  Good luck.

Robi

Vacuum guage needle is always flickering at idle. Valves are set at .019. Will a aftermarket cam cause this? Im thinking it should be steady.

Kenny  Onalaska, Texas