# How to ID quadrajet



## Icefan71 (Apr 7, 2011)

I was given a free carburetor today. It says Carter Quadrajet on the side. My friend doesn't know where it came from. He says its been sitting in a box in his garage longer than he can remember. It has the numbers 17058204. I found a website to decode it. 1978, fed emission standard, chevy, auto transmission. Underneath that number is 3197 BHT. I don't know what that means. Will a chevy carb work on a stock Pontiac 4bbl manifold? And how can I find out the air flow rating? I'm hoping I can use it on my 350. Thanks.


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## russosborne (Dec 6, 2010)

Try asking here.
Cliff's High Performance Quadrajets - Index
I think Cliff also has some stuff on his main webpage for id'ing carbs.
Russ


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## Icefan71 (Apr 7, 2011)

Thanks, Russ. I joined the forum there. Hope to get some answer.


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## chuckha62 (Apr 5, 2010)

The Quadrajet is designed and built by Rochester. As they became THE standard GM carb in the late 60's, Rochester Div. couldn't handle the volume, so they contracted with Carter to build them in parallel under license.

The Chevy carb. will work on the Pontiac, but the fuel inlet is different. The Chevy inlet is on the passenger side and the Pontiac is directly to the front. Almost without a doubt its a 780 CFM, as there were only a handful of 850's built and as I understand it, they were only offered on early 70's 455's. 

Cliff Ruggle's is THE Q-jet guy!


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## lars (Sep 28, 2004)

My Q-Jet Tuning Paper has all the Pontiac Q-Jet and Chevy numbers listed, along with all the correct jetting info - you can e-mail me a request for a copy. All Q-Jets are 750 cfm, except some Pontiac, Buick and Caddy carbs which were 800. The one you have is a 750. It's a carb for a 1978 350 Corvette, Federal emissions, with air and auto trans. It should be jetted 77/52/CH, and it's a very good performance carb if you are set up for the integral choke configuration (this carb cannot be used with a stock GTO divorced choke system). You will also need to re-do your fuel inlet line, since the Chevy carbs have the inlet on the passenger side, which does not make it easy to run a fuel line on a Pontiac.

Lars
[email protected]


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## lars (Sep 28, 2004)

chuckha62 said:


> Almost without a doubt its a 780 CFM, as there were only a handful of 850's built and as I understand it, they were only offered on early 70's 455's.


Here is the section from my tuning paper discussing Q-Jet sizes:

"Q-Jets were built in two sizes: 750 cfm and 800 cfm. Many of the Q-Jets were further limited in their actual flow rating using mechanical stops on the secondary airvalve shafts or on the secondary throttle linkage to prevent full opening of the secondaries, but any of these carbs can be corrected to flow the full rated capacity. Care should be taken when doing this to assure that the modification does not produce any binding of linkage pieces. The high-flow carbs use secondary airvalves that rotate through an 80-degree arc. Lower flow carbs have a stop which limits rotation anywhere from 60 to 80 degrees. Most carbs can be set up to produce an opening arc of up to 85 degrees, but should not be set to open any further than to the point where the lower edge of the airvalve points directly at the top edge of the secondary air baffle plate. On most secondary airvalve shafts with arc limit, the stop tab on the shaft can simply be filed down to increase the arc travel of the shaft. Again, be sure you do not induce linkage binding with the additional travel, and do not modify to produce “over-rotation.”

All pre-1971 Q-Jets are 750 cfm. In 1971, Pontiac introduced an 800-cfm carb for use on the 455 H.O. Ram Air engines. This was a unique design, used only in 1971, and only by Pontiac. It can be identified by looking at the venturi booster venturies: A “normal” Q-Jet has a booster ring (also known as the “Intermediate Ring”) that surrounds the center discharge tube and venturi. The 800 cfm 1971 Pontiac has no Intermediate Ring: Only the center discharge venturi sticks out into the main venturi: it looks like “it’s missing something” in the venturi.

Buick also had an 800-cfm Q-Jet in 1971, used on their 455s from 1971 through 1974. Buick took a different approach: Instead of eliminating the Intermediate Ring, Buick enlarged the outer bore size of the primary venturi, making the outside walls almost straight with no real “venturi shape.” The problem with doing this is that there are internal passages in one area of the venturi wall, so to make the walls larger and straight, Buick had to put a “bulge” in each of the outside walls. This makes it very easy to tell that you’re looking at an 800-cfm carb: Just look for the bulge. If looking at the carb from the front (fuel inlet towards you), the bulge in the driver’s side primary venturi is in the 2-o’clock position. The one on the passenger side is in the 10-o’clock position.

In 1973 and 1974, Pontiac used this Buick design 800 cfm carb on their 455 Super Duty engines.

These are the only 800 cfm divorced choke carbs built.

In 1975, the passenger car Q-Jets changed to the M4M design. All Pontiac M4M carbs are 800 cfm. Buick/Olds/Cadillac also made common use of the 800 cfm design. It is very rare to see a Chevy 800 carb – it was seldom used."


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## lars (Sep 28, 2004)

Icefan71 said:


> It has the numbers 17058204. Underneath that number is 3197 BHT. I don't know what that means.


The carb was built on the 319th day of 1977, making it a 1978 model year carb.

Lars


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## chuckha62 (Apr 5, 2010)

Good info Lars, Thank you. I had always understood they were 780 and 850, respectively. I stand corrected!


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## Icefan71 (Apr 7, 2011)

Wow, Lars. You know your stuff. Thanks for the info. I sent you an email.


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## Icefan71 (Apr 7, 2011)

Will the integral choke work if I just remove the coil assembly from my intake? Or is there more to it? If I can do this, I should be able to modify my fuel line or bend a new one. And of course I'll have to make sure the carb works ok. Oh yeah, and I have to get a 4 bbl intake.


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## russosborne (Dec 6, 2010)

If you want to come to Warren, Oh, I can give you a free intake. It is from a later 70's engine, so it has the egr-which most people don't like the look of. 
But you could probably come up with one around there for less than $100 also.
It was given to me, but then I ended up with an Edelbrock Performer I am going to use.
Russ


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## Icefan71 (Apr 7, 2011)

Russ, thanks for the generous offer. If I was a little closer to you, I'd take it, but you're over 4 hrs away. I'll just keep checking craigslist and ebay. One will pop up close by.


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## lars (Sep 28, 2004)

Icefan71 said:


> Will the integral choke work if I just remove the coil assembly from my intake?


No, the hot air integral choke is set up for hot air tubes that have to be hooked up to a 1975 - 1979 manifold. The '75 - '79 manifolds are not the best performing manifolds, so I would not recommend using one of those. To use the M4M carb with integral choke, you need to do an electric choke conversion and use the electric choke assembly from a 1980 Chevy Q-Jet or the one offered by Edelbrock for that carb.

Lars


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## Icefan71 (Apr 7, 2011)

Yeah, I sent an email to Cliff Ruggles and he also said I need an electric choke conversion. Its added to the ever growing list.


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