Snoopysvet

I want to check the air fuel mixture using a vacuum gague, where do i plug my vacuum gague?

jackwabbit703

If you have a QJET, look for nipples under the throttle plate on your carb like the one's with yellow arrows pointing to:



On mine, green arrow is ported vacuum since it was later style QJET. Earlier style I heard that port is full time manifold vacuum port.

There should also be another nipple on back of the carb next to brake booster vacuum port.

Snoopysvet

Thank You
Waskelly Wrabbitt!!

7T1vette

How to you "set" air/fuel mixture with a vacuum gauge? You can adjust the idle mixture screws for maximum vacuum at idle [assuming that you have set ignition timing in an appropriate manner and made all proper adjustments to the carb and choke system and that idle speed has been set]. But that approach assumes that A/F mixture is optimized by achieving maximum vacuum at idle. Usually, a mechanic will make a final 1/8 turn or 1/4 turn of those mixture screws toward the rich side, just to be sure it will not be running too lean.

There are a number of methods which could be used to set idle mixture. Maximum vacuum is one of them.

There is a manifold vacuum port that comes out the right side of the carb via a tube that sticks out through the choke mechanism. Prior to emissions systems, this was the 'normal' fitting that connected directly to the distributor vacuum can. But, any "manifold" vacuum fitting will work; ported, or timed, vacuum ports will not serve for this purpose.