Quadrajet Choke Circuit

Quadrajet 4 Barrel Primary & Secondary Pull-Off Type

This illustration is for a 1981 Chevy truck application. This particular carburetor uses both a primary, or front choke pull-off and a secondary, or rear choke pull-off. Starting in the mid 70’s, Quadrajet starting using this type of choke system and many of it’s 4 barrel carburetors.
The primary choke pull-off is tested by applying 15 lbs of vacuum to the inlet tube. The arm should pull in and stay there until vacuum is released.
The secondary choke pull-off will require 20 lbs of vacuum. You will also need to plug the relief hole (on the pulloff itself) if one is present. Same as above, the arm should pull in but will be slow moving. The secondary pulloff helps keep the secondary air valve open a bit so that the engine doesn’t run too rich when cold.

The particular Quadrajet uses an integral (mounted on the carburetor), choke thermostat.

Adjusting this type of thermostat.
Install the thermostat with a gasket, so that the tab D is up against the lever A. Twist the thermostat until the choke valve closes. You may have to hold the throttle open a bit so that it isn’t holding the choke open. When the choke closes, twist the thermostat another 1/8 to put a slight load on the valve.
As the thermostat heats up the thermostat coil will expand allowing the choke valve to open.
To test get the engine to operation temperature. The choke valve should be fully open.
B – This screw holds the choke housing to the carburetor.C – The retainer screws are sometimes riveted originally. Drill out the rivets and tap the holes, or use self tapping screws.

Divorced Choke
Integral Choke
Updated on 12/14/2020

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