Q-Jet Accelerator Pump Questions
Thread Starter
Instructor
Joined: May 2023
Posts: 153
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From: The Alamo, Texas
Q-Jet Accelerator Pump Questions
Hello y'all, I have a couple questions regarding my 1974 L-82 Quadrajet's accelerator pump. I'm becoming more convinced that something may be wrong with it.
- What exactly does the accelerator pump do? When does it activate? Does it send a stream of gas at all time when car is running? Or only when pedal is depressed?
- I have read that when twisting the throttle, I should see a "steady stream" of gas flow out. Should this happen when cold or running? For me, when car is cold nothing shoots out, when running it sprays out, when warm it dribbles out. This doesn't seem right.
- With a bad accelerator pump, I assume that means the little rubber cup has broken. If this is the case, would fuel evaporate out of the bowl? Perhaps this is my gas smell. Perhaps this is why on a cold start it has to crank for 4ish seconds to pump fuel into the carb.
- The install of the accelerator pump doesn't look to difficult. I can't find a new one from any major vendor, nor the upper carb/airhorn gasket. Any suggestions? Ebay new-old-stock delco parts?
Last edited by OrangeC3ButImAnAggie; Dec 2, 2023 at 12:40 PM.
1967 Pedal Car Champion
Joined: Mar 2020
Posts: 9,130
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From: US-PNW
#2: The steady stream is seen with the engine off, hot or cold. When the engine is running you may see a small bit of it but the rush of air going past aerosol-izes it pretty quickly, so you lose that strong liquid stream.
Race Director
Joined: May 2006
Posts: 18,728
Likes: 2,579
- What exactly does the accelerator pump do? When does it activate? Does it send a stream of gas at all time when car is running? Or only when pedal is depressed? Only when pedal is depressed
- I have read that when twisting the throttle, I should see a "steady stream" of gas flow out. Should this happen when cold or running? For me, when car is cold nothing shoots out, when running it sprays out, when warm it dribbles out. This doesn't seem right. Cold, hot, off, on when you open throttle. No movement no spray.
- With a bad accelerator pump, I assume that means the little rubber cup has broken. If this is the case, would fuel evaporate out of the bowl? Perhaps this is my gas smell. Perhaps this is why on a cold start it has to crank for 4ish seconds to pump fuel into the carb. Should not have smell from bad pump piston
- The install of the accelerator pump doesn't look to difficult. I can't find a new one from any major vendor, nor the upper carb/airhorn gasket. Any suggestions? Ebay new-old-stock delco parts?
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,171
From: Hermosa
Cliff's has the part you need. Don't get just any accel pump diaphragm. Cliff's are ethanol resistant.
https://cliffshighperformance.com/
https://cliffshighperformance.com/
1967 Pedal Car Champion
Joined: Mar 2020
Posts: 9,130
Likes: 4,243
From: US-PNW
I've ordered gasket sets from Mike's with good results: https://www.carburetor-parts.com/
If I had known that Cliff Ruggles sells parts I would have definitely ordered from him -- which I'll do from now on.
Cliff's has the part you need. Don't get just any accel pump diaphragm. Cliff's are ethanol resistant.
https://cliffshighperformance.com/
https://cliffshighperformance.com/
Tech Contributor
Joined: Aug 1999
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From: At my Bar drinking and wrenching in Lafayette Colorado
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
Your Accelerator pump adds an extra shot of fuel to give the engine a head start to rev before it can draw fuel through the boosters........it operates everytime and only when you hit the throttle......
I keep at least two Cliff's Q-Jet pumps in my box.......
I get at least that many customers with dead pumps every year.......
Jebby
I keep at least two Cliff's Q-Jet pumps in my box.......
I get at least that many customers with dead pumps every year.......
Jebby
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Dr. Detroit
Joined: Mar 2012
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From: New Braunfels Texas
Jebby
Tech Contributor
Joined: Aug 1999
Posts: 14,379
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From: At my Bar drinking and wrenching in Lafayette Colorado
I think one of the posts that Jebby is referring to may be this one. It has some photos and narrative that may assist you.
https://www.corvetteforum.com/forums...980-q-jet.html
Lars
https://www.corvetteforum.com/forums...980-q-jet.html
Lars
Thread Starter
Instructor
Joined: May 2023
Posts: 153
Likes: 35
From: The Alamo, Texas
Follow up: Ordered a new accelerator pump, airhorn gasket, and fuel filter from Cliff. Installed the parts using Lars' excellent instructions. The old pump was literally in pieces in there. Now I see how the fuel stream from the pump y'all are talking about is really supposed to look like! Before it just sort of dribbled out. Thanks everyone.
Pro
Joined: Nov 2023
Posts: 701
Likes: 335
From: Aubrey TX
Lars Grimsrud has a good white paper on the Q-Jet. He recommends NAPA part number 2-4055. This is an ethanol-resistant pump that works very well. I used it to replace the pump in my carb.
The paper itself is a little wordy but its complete and worth reading if you plan on keeping the Q-Jet.
Send him an email requesting his Q-Jet papers and he'll reply with them attached v8fastcars@msn.com
The paper itself is a little wordy but its complete and worth reading if you plan on keeping the Q-Jet.
Send him an email requesting his Q-Jet papers and he'll reply with them attached v8fastcars@msn.com