Quadrajet Manifold & Ported Vacuum Ports?
October 18th, 2010, 08:28 PM
#1
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Quadrajet Manifold & Ported Vacuum Ports?
Just got an 800 cfm Quadrajet from SMI carbs and I want to hook up a vacuum gauge to work on the idle mixture adjustment. I use a dual-plane intake that doesn't have a common port for total manifold vacuum from both planes. I realize the PCV and power brake ports on the carb are full manifold vacuum, but those are large size ports (3/8") that are hard to "tee" into for a vacuum gauge with 3/16" line. Is there another port that is a manifold vacuum source on the carb itself? Also, which port is "ported or timed vacuum" for the distributor vacuum advance? If any of you have a picture or diagram you could post that would be sweeeet!
October 19th, 2010, 05:49 AM
#2
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To find a manifold vacuum port on your carburetor all you have to do is put your finger over the port when the car is idling. If you feel vacuum at the port when the car is idling then the port is manifold vacuum. If there is no vacuum at the port when the car is idling then the port is ported vacuum.
October 19th, 2010, 06:05 AM
#3
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You shoud be using the same one for the vacuum advance, as that should be disconnected for carb adjustments anyway.
Highest vacuum @ idle is best, then plug in the vacuum advance and adjust RPM.
Highest vacuum @ idle is best, then plug in the vacuum advance and adjust RPM.
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