Engine Vacuum

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Mar 25, 2008
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So I installed an edelbrock EPS manifold and Edelbrock 600 cfm.

Interestingly I lost engine vacuum. The single plane pulled 15lbs of vacuum, the dual plane pulls 12-13lbs of vacuum.

Unfortunately it still backfires off if I give it alot of gas off of idle.
 
There is a vacuum leak in the accessory vacuum circuits, and PCV.
 
What year is your car? The alter AC controls (slider) is notorious for leaking.
 
1973

I have the PCV circuit, the interior accessory circuit, and the headlight circuit with that big canister down in the fender.

So as a dumb question, if I have a PCV valve on one valve cover and a breather on the other, would that create the vacuum leak? SHould I plug the other valve cover hole instead of having a breather?
 
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