how do I know what I got?

I have a couple of Q-jet carbs, how can I tell how many CFM they are rated for, and which one would be better for performance? One is claimed to be from a 68 400 and the other one I have no idea what it came off of originally. Thanks for any help in identifying these carbs. o No:

 

Here is how to decode the numbers on the driver's side of the carb:

Rochester Number decoding


Example: # 7028219
DG 1938

7028219
Prefix code. "70" will appear on all late '60's Rochester Carburetors.
76 and later will start with "170"
2 - Decade produced.
702 - 1960's
703 - 1060's with A.I.R.
704 - 1970-1975
1705 - 1976-1979
1708 - 1980's
7028219
Year produced.
8 = 1968
If the number was 7045219 then
5 = 1975
7028219 Model
0 - Monojet (1 bbl) Federal standards
1 - Two jet (2 bbl) Federal standards
2 - Quadrajet (4 bbl) Federal standards
3 - Monojet (1 bbl) California standards
4 - Two jet (2 bbl) California standards
5 - Quadrajet (4 bbl) California standards
6 - VariJet (2 bbl) Fed
7028219 - Division.
0, 1, and 2 all indicate Chevrolet.
4 - Buick
5 - Olds
6,7 - Pontiac
7028219 - Transmission
Even numbers - Automatic Transmission
Odd numbers - Manual Transmission
DG Production Plant Code.
1938 Date Code
193 = 193 rd Day of the year
1938 8 = Year


Here is also a page to help you:

http://buickperformance.com/qjet.html

 

Thanks Phillip, that information is very helpfull.

 

I saved this picture that Bill Stacy from BuickStreet.com posted a looong time ago showing the bump identifying the 800 cfm Q-Jets.

 

Here's another good view from Doug Roe's book "Rochester Carburetors".



Devon

 

Thanks guys, good info. Here are the numbers from the two Q-jets.

7028244 according to the page supplied by Phillip this is a 750 CFM from a 1968 buick 350 CID. I looked and the primary jets are 70's and the secondary rods have the code AY.

7043240 which is a 800 CFM from a 1973 buick 455 CID. The primary jets are 78's and the secondary rods have the code CF.

Any info about the codes on the secondary metering rods? o No:

I think I'll try to use the 800 CFM Q-jet , looks like it could use a rebuild, where is a good place to pick up a rebuild kit with the correct manifold gasket, you know the one that is about 1/4" thick, mine is shot :blast: .

 

http://www.hioutput.com/tech/qjetrod.html

http://buickperformance.com/qjet.html

http://peterpam.customer.netspace.net.au/quad.htm

Gotta love Google!

Devon

 

Thanks for all the help guys.

At least someone knows how to use their computer, I can't even figure out how to set the idle on mine :laugh:

 

So I finally got around to rebuilding the 800 CFM carb. It feels like a different car. Runs much better. Still need to do a little tweaking , it has a slight stumble when the secondaries open (tighten the spring). Thanks for all the help.

 

Slight stumble can be caused by:

Secondary vacuum brake being bad
Secondary cam for lifting metering rods is broken or missing a piece
Adjust secondary coil spring for better/slower opening rate

 

Secondary bog/hesitation is often caused from a fatigued air valve spring. Both the airvalve spring and the secondary airvalve plastic cam should always be replaced at any major service of the carburetor.

Jon.