vacuum


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By 62galxe - 14 Years Ago
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.
By Hutz 292 - 14 Years Ago
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

By oldcarmark - 14 Years Ago
How much does it vary in inchs of vacuum?Does it appear to be random or at regular intervals?
By 62galxe - 14 Years Ago
idle it is between 11 to 14. overlap shows 48 deg on the cam card. It flickers at all rpms.
By Ted - 14 Years Ago

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.

By Hoosier Hurricane - 14 Years Ago
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?