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Old 01-14-2013, 10:50 PM
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cobalt327 cobalt327 is offline
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You're quite welcome. There is a guy, "Lars" who has also posted extensively on the Q-jet. He knows his stuff. Below is one of his posts (there are other pages by him if you do a search).

From Quadrajet Info by Lars:

Plugged accelerator pump transfer holes in air horn
Results in: Off-idle stumble or hesitation, hard cold-start.
Comments: There is a tiny transfer hole that runs horizontally in the air horn, just inside of the actual accelerator pump discharge orifice. It is common for this to be plugged with some type of debris, especially in carbs that have been sitting around for a while. If this passage is plugged, there will not be any accelerator pump shot.

Jammed accelerator pump check ball
Results in: Off-idle stumble or hesitation, hard cold-start.
Comments: This is a common problem in carbs that have been allowed to “dry out” for a while. Sediment in the bottom of the fuel bowl will lock up the check ball as if it were set in concrete. This will prevent any accelerator pump discharge.

Accelerator Pump Rod Installed in Wrong Hole in Pump Arm
Results in: Off-idle stumble or hesitation.
Comments: There are two holes in the accelerator pump lever arm for the lever arm rod to engage into: Inner and Outer. The outer hole produces a leaner pump shot, and can cause a lean stumble on engines requiring a robust pump shot. Corvettes and performance cars always used the rich, inner pump arm hole.

Jammed accelerator pump
Results in: Off-idle stumble or hesitation, hard cold-start.
Comments: This is becoming a common problem. The alcohol additives in modern fuels are not compatible with the materials used in many accelerator pumps (even some of the pumps in brand new carb kits). This causes the pump plungers to swell up and to seize in the pump bore. The spring on the pump shaft still allows the shaft to move up and down, making it look as if the pump is functioning. But the pump itself can be seized up solid in the bore with the shaft working just fine. To fix this, you must install a pump that is specifically compatible with alcohol.

Worn accelerator pump
Results in: Off-idle stumble or hesitation, hard cold-start.
Comments: Common on older carbs and on carbs that have been allowed to dry out (vehicles stored without being started through the entire winter season). The rubber plunger material will dry out and shrivel up, making the accelerator pump completely ineffective. The pump must be replaced.
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