vacuum test

[Walter R.]

I have a rough running BB recently rebuilt and have checked everything I know to check. I have an afterrmarket Holley on original intake and ran vacuum test on V line at throttle plate base. Vacuum ran 12 B. I understand the manifold vacuum should be close to 18-20. Should I see this kind of difference.

[John H.]

Re: vacuum test

I have a rough running BB recently rebuilt and have checked everything I know to check. I have an afterrmarket Holley on original intake and ran vacuum test on V line at throttle plate base. Vacuum ran 12 B. I understand the manifold vacuum should be close to 18-20. Should I see this kind of difference.

Walter -

Which BB do you have, and what's your idle rpm? There's a marked difference in manifold vacuum between the hydraulic and solid-lifter engines.

[Duke W.]

Re: vacuum test

Year, engine option, and transmission. Did you have an OE replacement cam installed or some bubba cam?

Manifold vacuum is measured in "inches of Mercury" - usually denoted as "Hg. I have no idea what you mean by "12 B".

Idle vacuum readings without specfiying idle speed (in neutral for manual transmissions and Drive for automatics) is useless.

Duke

[Robert G.]

Re: vacuum test

Here is a web site that shows various vacuum related problems.

http://www.secondchancegarage.com/public/186.cfm

[Stephen B.]

Re: vacuum test

Robert
Great advise. I've been using a vacuum gage since I was a pup,and found it to be one of the most valuable tune up tools in my box. They are excellent for diagnosing problems as well . Those reading this that want to throughly understand what you engine is doing should invest in one and become familiar with it and your engine.Generally speaking they only cost about 15 or 20 dollars.
Stephen Barrett (21558)