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#1
12-15-2012, 04:18 PM
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Need some vacuum connection help...
My 72' Monte Carlo, factory J code 350 4bbl car. I removed the efi and am putting it mostly back to stock. I have a few questions... What connects to the port on the back of the Quadrajet? (It is a factory 72' #7042202 350/th350 carburetor) Where does the vacuum advance on my distributor connect to? And lastly, where should the vacuum line from the transmission connect to?
TIA
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1972 SS 454 Chevelle LS5/M21/12 bolt 3.73 posi 1969 Malibu COPO L72/M20/12 bolt 3.31 posi 1968 Malibu LQ9/4L80E/12 bolt 3.73 posi 
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#2
12-16-2012, 04:23 PM
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Not seeing the carb, but the vacuum port in the back could be for your distributor and your trans.
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Ray 1970 SS Chevelle Van Nuys Built
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#3
12-16-2012, 08:36 PM
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Right now, there is a brass plug in the carb. I bought it that way, but believe there should be a vacuum nipple there. I found a few diagrams online, but they are vague and the illustrations are horrible. From what I can tell, the vacuum advance goes to a port on the front of the carb. Still unsure about the rest.
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1972 SS 454 Chevelle LS5/M21/12 bolt 3.73 posi 1969 Malibu COPO L72/M20/12 bolt 3.31 posi 1968 Malibu LQ9/4L80E/12 bolt 3.73 posi
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#4
12-17-2012, 08:40 AM
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My diligence may have payed off... these pictures show plenty of detail. I am going to post pictures and links here in hopes that it may help someone else in the future.
  The thread these pictures are from can be found here: http://forums.corvetteforum.com/c3-t...ng.html?nojs=1 Courtesy of the Corvette Forums.  It appears the connection on the back of the carburetor goes to the brake booster. And the manifold supplies vacuum for the A/C and shift modulator. Also in the photos are the connections for PCV and the vacuum advance.
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1972 SS 454 Chevelle LS5/M21/12 bolt 3.73 posi 1969 Malibu COPO L72/M20/12 bolt 3.31 posi 1968 Malibu LQ9/4L80E/12 bolt 3.73 posi
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#5
12-17-2012, 09:19 AM
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Both the large port on the back of the carb and the port on the intake manifold are "manifold vacuum" ports which you want for brakes, transmission, Vacuum advance, valve cover, etc. The smaller ports you see on the carb, one of them is usually "manifold" and the other "ported". You would want the vacuum advance can connected to the "manifold" vacuum. You can check this with a vacuum meter. the "ported" won't have any vacuum at idle and the "manifold" port will.
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#6
12-17-2012, 02:58 PM
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Typically the large one at the base of the carb in the rear is used for brake booster. There may be a small one near the base on the front side, and another one, a little larger, near the base of the carb in front. The larger one in front is for the PCV. The small one can be T'ed for vacuum advance and trans.
The engine in the pic has a port threaded into the manifold. You can use that for vacuum advance, trans, brake booster as well and cap the ports on the carb.
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I pretty much have it licked. 
Linear Mode
