I was just wondering what the feelings are on a Carter carb versus a Rochester. Our 70 had a Carter on it when we bought it. I don't feel our gas mileage is all that hot from what I hear others get, but the performance seems fine. Maybe it would be peppier & improve mileage with the Rochester on it. Just trying to get some thoughts on the idea. Thanks.

 

Can of worms = opened

I'll keep it simple, though.

The carter afb was designed in like the 50's I believe and was like a 450 or so cfm carburetor at first. It was eventually enlarged to flow more cfm but it wasn't very big at first. It was pretty simple and most people understand how they work.

The rochester carburetors (q-jet, dualjet, and fomg the monojet!) were designed, initially, in the 60's and are much more precise in fuel metering. The basic goodies, that the q-jet has over the carter, are that it's essentially a variable cfm carburetor (they were used on V6s up to 500ci caddy engines and big chrysler engines), they come in 3 sizes 750, 795, and 850 cfm (large, XL, and XXL basically), and they work a hell of a long time without needing to be tinkered with. They're probably the least understood of any carburetor but are one of the most efficient, once tuned. Their efficiency is only surpassed by later carburetors such as Weber, Mikuni, and CVK. The second two are mainly used on motorcycles now, while weber is mainly a racecar or custom application carb.

Both carburetors do their job of mixing fuel with air and shoving it in the engine, but the quadrajet requires more fine tuning to get it running good. Basically simplicity vs. complexity but neither are really very complex at all.

Many hate the q-jet and many love it (I know I do ) I think there's a wikipedia about it, check it out.

 

In 1969, and possible in 1970 Rochester was unable to supply a sufficient number of carburators and GM called upon Carter to produce the QuadraJet so there was Corvettes with Carter built QuadraJets. These was designated on the Protect-O-Plate by the letter, C for Carter carburetor, so maybe it is the original carb you have.

 

Carter built Quadrajets for GM well after 1969... at least up to 1973
All 1970 Corvettes came from the factory with either the Quadrajet or a Holley
Carter Quadrajets are no different then the Rochester

If you have something other than the Carter QJ or the Holley then I would think about a swap.

Can you post the stamped number of your carb?

 

the numbers i can see:7029202 and under this number:A9 DH
And above the QuadraJet cast: MDF.BY
CARTER
CARBURETOR
FOR GMC

 

That is indeed a 1969 Quadrajet built for an automatic trans
I suggest you keep your paws on that one
What transmission/engine/rear end ratio ?
Also, what are you getting for milage
I can squeeze 18 or 19 MPG at 60-65 MPH
If I play around I will be lucky to see 12 MPG
Keep in mind I have the 3.08 gears and only turn 2,700 RPM at 70 MPH

 

This carb is laying in my garage, not on the car. The engine in my car is a non original 350 and automatic trans, 3.36 gears. Here in Norway the gas cost almost 2$ for 1 litre, so i think the best is that i dont know the MPG

 

Sorry
Somehow I got confused as to who the original poster was
The thread was started by Amature (thats the persons name)

Now Im very confused
Anyhow....corvald
What carb is on your engine at the present time?

 

the carb in my vette now is a Rochester with #17058212. I dont know what car it original was on, but its not Corvette?? Its nice for my driving, I also have two Holly carbs, one 650 and one 600. The 650was too big i think. The 600 was nice on driving, but i had problem with the idle, but i am not a mechanic, so i think its only tuning it need.

 

Is there any truth that Edelbrock took over Carter.....

 

yes

 

Hmmm, I've never heard of a 850 QJ?

I'm aware that Buick/Olds had the 800 QJ though?

What are the details on the 850 QJ (what was it used in, how to ID it etc)?

Agree that the Q-Jet simply the best mass produced street carb made (get 19MPG out of my 375HP 406 at cruise with 700R4 and 3.08's, and run 12.87 @ 112MPH at 330ft).

One advantage of the AFB design is that the Primary Rods can be swapped easily if you change altitude often (it's the Secondary Rods that swap easily with the QJ, which is good for the strip). I've also heard that AFB's have a problem with high G (lateral I think?), so they're likely not so good on the track (but fine on the street).

Doug

 

No ones mentioned the main reason for the good MPG....... go on.tell him !!

 

I just had a chance to check out the Carter carb numbers on our car. they are 7040203 H9(c) DB. I know the number signify 70- 350, 300 hp, manual 4 sp. I'm guessing the H9 must be a date code, the DB, I don't have a clue. Engine wise, my car appears to have been assembled March 2, 1970. I don't know what the gear ratio in the rear axle is but our mileage is roughly around 15 mpg. Where we generally driv, the are some 70 mph and some 45 - 55 mph. The carb appears to be leaking slightly in the front. Probably time for a rebuild. The car was restored to NCRS Top Flight about 11 years agp by the previous owner.

 

Not quite
70= Rochester (or Carter built Rochester)/ 40= 1970/ 2=49 State, Not a California carb/ 0= Chevrolet and the 3 = Manual transmission