Cliff's Quadrajet Parts and Rebuild Kits

General Category => Quadrajet Carb Talk and Tips => Topic started by: Spudboy on December 19, 2009, 11:01:48 AM

Title: Quadrajet rear vent
Post by: Spudboy on December 19, 2009, 11:01:48 AM

  I have a question on the Q-Jet rear vent. All of my Pontiac carbs from 68-71 have this in operation with the bi-metal strip and cover. I have a Buick 7041540 carb that I am switching to Pontiac use by swapping
the throttle shafts and choke setup. Since it will now be used on a Pontiac, would it be wise to open the
passages and run the Pontiac rear vent setup?

Title: Re: Quadrajet rear vent
Post by: Schurkey on December 19, 2009, 02:00:02 PM

Quote from: Spudboy on December 19, 2009, 11:01:48 AM

  I have a question on the Q-Jet rear vent. All of my Pontiac carbs from 68-71 have this in operation with the bi-metal strip and cover. I have a Buick 7041540 carb that I am switching to Pontiac use by swapping
the throttle shafts and choke setup. Since it will now be used on a Pontiac, would it be wise to open the
passages and run the Pontiac rear vent setup?

I'd wait and see if you had problems with hot idle.

Title: Re: Quadrajet rear vent
Post by: Cliff Ruggles on December 22, 2009, 04:26:47 AM

The rear vent is actually the HIC, or Hot Idle Compensator.  It was used to provide a controlled vacuum leak when underhood temperatures reached a determined point, or high enough point to cause the bi-etallic spring to open the valve and add some addtional air at idle speed.

I don't usually leave this system in place for high performance carburetor builds, but will on stone stock set-ups if the parts are still in good shape......Cliff

Title: Re: Quadrajet rear vent
Post by: Spudboy on December 22, 2009, 09:42:59 AM

Thanks for the info.