Quadrajet Question
Thread Starter
Cruising
Joined: Sep 2015
Posts: 10
Likes: 0
From: League City Texas
Quadrajet Question
Evening everyone. I'm looking to purchase a rebuilt quadrajet for my 1975 L82. Just lookin to freshen things up before I do serious engine work and the current carb is in poor shape. I've noticed a few sites say the almost identicle looking carb isn't compatible for my L82. All the emissions equipment was removed by a previous owner and I'm just a bit puzzled on what carb I can purchase without making an uneducated guess...
Race Director
Joined: Apr 2003
Posts: 19,353
Likes: 654
From: Tampa, Florida
Start with the number off the carb and find what it's from. Do NOT buy one from a truck.
You could always have yours rebuilt. If you have reasonable skills buy the Ruggles book, combine it Lars' papers and do it yourself.
Remember, smart people always say 90% of all carb problems are really ignition problems....and it's true.
You could always have yours rebuilt. If you have reasonable skills buy the Ruggles book, combine it Lars' papers and do it yourself.
Remember, smart people always say 90% of all carb problems are really ignition problems....and it's true.
Drifting
Joined: May 2012
Posts: 1,353
Likes: 44
From: Calgary Alberta
Do not buy a commercially rebuilt quadrajet. It's not worth your time and money to do that. They are often a mixed bag of parts, and that makes tuning them nearly impossible. Quadrajets were, from the factory, application specific.
If the quadrajet on your car is in decent shape but just running sub-par, absolutely try rebuilding it. It's actually pretty easy - really it is. You just need a kit and a good way to clean the thing up. This is also by far the cheapest option probably.
If the quadrajet on your car is in decent shape but just running sub-par, absolutely try rebuilding it. It's actually pretty easy - really it is. You just need a kit and a good way to clean the thing up. This is also by far the cheapest option probably.
Advanced
Joined: Sep 2015
Posts: 74
Likes: 6
From: oregon
Totally agree with first 2 post. If you decide to try a rebuild yourself I would first disassemble carb and do an assessment on the condition of the parts. Now you can order a kit and any misc parts you think need to be replaced.
I also bought a used $30 carb from craigslist to use as a road map. Worked for me and am very happy with the results. Good luck.
I also bought a used $30 carb from craigslist to use as a road map. Worked for me and am very happy with the results. Good luck.
Le Mans Master
Joined: Oct 2007
Posts: 7,459
Likes: 979
From: RI, Now Franklin/Nashville TN
All good advice^. Do not buy a rebuilt...most are junk. I would:
1. Rebuild it yourself if you can
2. Send it to Lars for a rebuild if you can't do #1
3. Buy a NEW Holley 4175 650 CFM vacuum secondary Q-jet replacement carb (made to replace the Quadrajet)...I have had a 4175 on my 78 L-82 since 1985 (rebuilt it for the first time in 2010) and currently being used on the rebuilt L-82 with AFR heads and Roller cammed L-82 355....works great on the rebuilt engine as well with minor jet changes.... Great carb!
1. Rebuild it yourself if you can
2. Send it to Lars for a rebuild if you can't do #1
3. Buy a NEW Holley 4175 650 CFM vacuum secondary Q-jet replacement carb (made to replace the Quadrajet)...I have had a 4175 on my 78 L-82 since 1985 (rebuilt it for the first time in 2010) and currently being used on the rebuilt L-82 with AFR heads and Roller cammed L-82 355....works great on the rebuilt engine as well with minor jet changes.... Great carb!
Last edited by jb78L-82; Feb 12, 2016 at 07:16 AM.
Pro
Joined: May 2006
Posts: 596
Likes: 84
From: Colonial Beach Virginia
Rebuilding is surprisingly easy. Take your time and you'll nail it. I always rebuild my carbs on top of a stretched out towel (lint free of course) so that the small parts do not get away from me if dropped. Just a thought.
Le Mans Master
Joined: Jul 2006
Posts: 8,117
Likes: 104
From: charlotte north carolina
As posted above, rebuilding your carb is the best option. However, an even better idea is to spend $30 and buy the worst looking POS carb that reasonably matches your carb that you can find on ebay (assuming it is intact) and disassemble it first. That way, you'll gain experience in dis-assembly and possibly have a few spare parts such as down tubes, shafts and springs. And, you'll end up with a carb body that can be used as a test-bed for calibrating power pistons.
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Tech Contributor
Joined: Aug 1999
Posts: 14,382
Likes: 6,401
From: At my Bar drinking and wrenching in Lafayette Colorado
If you're not concerned about "numbers-matching," don't use the '75 carb. The '75's don't have the adjustable APT (power piston height), and they utilize a non-needed rear choke pulloff. Rather, find any used (not rebuilt) 1976 - 1980 Chevy passenger car carb. Many of these are actually 800 cfm carbs (the usual is 750), but any of them can be rebuilt and set up to run very well. There are a lot of them for sale on eBay, but quite a few are junk or commercially rebuilt carbs. For more info, you can e-mail me for info on commercial carbs and info on my "carb screening service."
Lars
V8FastCars@msn.com
Lars
V8FastCars@msn.com
Melting Slicks
Joined: Apr 1999
Posts: 2,675
Likes: 13
From: Sudbury MA
I sent my quadrajet to Lars years ago for my 68 and it still runs like it just came from the factory. He is a genius and knows these carbs inside out. Cheapest and best route in the long run.
Kurt
Kurt
Le Mans Master
Joined: Sep 2003
Posts: 8,812
Likes: 2,029
From: eastern NC
Here's one for a '73 Corvette... (near Raleigh)
750 CFM Quadrajet Carburetor 1973 Chevy C3 Corvette
https://raleigh.craigslist.org/pts/5434231009.html
Good luck... GUSTO
750 CFM Quadrajet Carburetor 1973 Chevy C3 Corvette
https://raleigh.craigslist.org/pts/5434231009.html
Good luck... GUSTO
Tech Contributor
Joined: Aug 1999
Posts: 14,382
Likes: 6,401
From: At my Bar drinking and wrenching in Lafayette Colorado
The '73 Q-Jet is a 4MV carb. The '75 Vette uses an M4M. The two carb models are not directly interchangeable. He needs a '75 - '80 carb as noted above, and I'd suggest not using the '75 for reasons stated. If using the '73 4MV, the choke would need to be disabled, or the intake would need to be changed.
Is the carb damaged? What makes the carb "in poor shape?" If the carb is original, undamaged, and not a commercially rebuilt carb, it's probably the best candidate you have for a nice setup on your car.
Lars
Is the carb damaged? What makes the carb "in poor shape?" If the carb is original, undamaged, and not a commercially rebuilt carb, it's probably the best candidate you have for a nice setup on your car.
Lars
Last edited by lars; Feb 14, 2016 at 12:16 AM.
Drifting
Joined: Jul 2012
Posts: 1,255
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From: Slovenia, EU
2017 C3 of Year Finalist
When we are here with the debate on Qjet. I checked the numbers on mine (71 vette with 350 engine) and guess what? It's from a truck!!!! Now I'm looking at Holley 4175 but I do have performer RPM intake on the engine. Does anyone have any experience with this configuration?
Le Mans Master
Joined: Oct 2010
Posts: 6,943
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From: melbourne florida
2023 C3 of the Year Finalist - Modified
A performer RPM is a square bore intake making an adapter necessary for the 4175 and the quadrajet it just makes everything taller. Something like a holley 3310 would be able to handle just about anything you ever do with that engine and would run very nicely.it is not too big a carburetor in spite of what some may say.another option is quick fuel they make a good product.there are some carbs that look to me like they are modeled after a thermoquad but I have no experience with them. They seem to gimmicky for my taste.
Drifting
Joined: Jul 2012
Posts: 1,255
Likes: 297
From: Slovenia, EU
2017 C3 of Year Finalist
A performer RPM is a square bore intake making an adapter necessary for the 4175 and the quadrajet it just makes everything taller. Something like a holley 3310 would be able to handle just about anything you ever do with that engine and would run very nicely.it is not too big a carburetor in spite of what some may say.another option is quick fuel they make a good product.there are some carbs that look to me like they are modeled after a thermoquad but I have no experience with them. They seem to gimmicky for my taste.
Le Mans Master
Joined: Oct 2010
Posts: 6,943
Likes: 850
From: melbourne florida
2023 C3 of the Year Finalist - Modified
I have a quick fuel carb on my car,in 4 years it has been flawless and easy to tune.it is every bit the equal of holley and may in fact be better.
Tech Contributor
Joined: Aug 1999
Posts: 14,382
Likes: 6,401
From: At my Bar drinking and wrenching in Lafayette Colorado
There's nothing wrong with the pre-'75 4MV (divorced choke) truck carbs - they are the same as the passenger car carbs in most cases and can be set up to run just fine. The 1975+ M4M light duty truck carbs are not good candidates for use on passenger cars due to the "fat-tipped" primary rods and the air bleed systems set up for low-rpm trailer-lugging operations.
Lars
Lars
Pro
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From: Mainz