Service- Testing Choke Pulloffs

The choke pulloff is a critical component of the Rochester Quadrajet carburetor. It affects choke operation and secondary air valve operation. Some Quadrajets have only the front pulloff while others have both the front and rear pulloffs, a few came with only the rear pulloff.

The pulloff has 2 functions:

• On cold startup the choke flap is fully engaged/closed for maximum richness to allow easy cold starting. Once the engine starts, engine vacuum will be applied to the choke pulloff and its plunger will be retracted, opening the choke a little for a less rich mixture to keep engine running properly.
   
• The pulloff plunger also controls the secondary air valve opening rate. When wide open throttle (WOT) is applied, the engines manifold vacuum is reduced significantly and the pulloff begins a controlled release of its plunger. This controlled release is what partially controls the opening rate of the secondary air valves.

Recommended procedure for testing a front or primary pulloff and rear or secondary pulloff.

Checking with hand held vacuum pump:
1) Determine if the choke pulloff has a built-in air bleed (leak). If it does, it must be plugged prior to testing.  Most rear pulloffs have an air bleed.  Most front pulloffs do not have an air bleed.

2) Using a hand held vacuum pump, apply 15" Hg vacuum to the choke pulloff.
The pulloff plunger should move full travel. Apply finger pressure to plunger to verify that it has moved though its full travel. If it has not, replacement is required.  The choke pulloff diaphragm should hold for at least 20 seconds.

Checking on the running engine:
1) Apply engine vacuum to pulloff (At least 15" Hg) It is not necessary to plug air-bleed if so equipped. The pulloff plunger should move full travel. Apply finger pressure to plunger to verify that it has moved though its full travel. If it has not, replacement is required.