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Which Q-Jet

3K views 7 replies 6 participants last post by  slopoke 
#1 ·
I'm looking at getting a rochester q-jet but dont know which to get. I did a search and all i found was look for mid to late 70's GM V8. Is this information correct, or is there another year and model i should be looking for. And abotu the yeear and model im looking for, what is better about that model qjet then the others.
thanks
Andrew
 
#2 ·
I'm in the same boat right now. I want to rebuild the q-jet on my 350sbc until I can afford to finish my EFI. It is the 1973 model that was originally on my engine, electric choke, no emissions crap. Is it a good candidate? I'm no good with carbs and there's a guy in town here who lives and breathes q-jets who can make them run great for $75, including parts.

J. J.
 
#4 ·
I would be very suprised if the holley could ever hang with a properly dialed in Q-Jet. I have never owned an avenger but the bowl setup on holleys is just not cutout for steep angles. I have run regular holleys, edelbrocks, carters, and Q-jets and in my opinion the Q-jet spanks any of these. I have heard that the Avenger still has problems on very steep inclines. Have you had any problems with yours when your angled up steep.
 
#5 ·
slopoke said:
get the new holley truck avenger carb, i got it and love it, works great on hills and the power is amazing over my old q-jet carb.
The Avanger is not an option for me as the q-jet is just a temporary fuel system ... I'm just waiting on the money to complete the partial EFI that is sitting on my parts pile. I'm not about to cough up $400+ for an Avenger to throw away.

J. J.
 
#6 ·
Uh, Dude, what happened to your carb?

Hey Andrew, Unless I've been smokin' the crack-pipe entirely too much lately (possible), don't you already HAVE a q-jet on your junk? As I remember wasn't it an Edelbrock Q-Jet (I think that's what I remember, but I could be off base, I'm not a v-8 guy).

You might want to snap some pics and post for positive ID first.
 
#7 ·
Hope this info helps. I will post more if I find it.


Rochester Quadrajets


This discussion is limited to the period from 1962 to 1975 for several reasons: in 1963 Rochester part numbers started to make sense and by 1975 GM was producing many different engines, the feds and California each had their own, and the numbering system changed in 1976 so it is a good place to stop.

To begin with, Rochester separates carburetors into groups - a 2GC goes in the center of a tripower, a 4MC is a Q'Jet. Right.

The groups are easy to figure out: the first number indicates the number of barrels (one barrels leave the number off), the next letter is the venturi type: In this period Rochester produced B (one barrel), G (two and four barrels), and M (Monojet/Quadrajet) series in this period. The last letter indicates if a choke is used: no letter for none or manual choke (tripower end carbs were 2Gs), C for an automatic choke with the coil mounted on the carburetor and hot air tubes leading to the carb., V has a vacuum brake and the choke coil is mounted on the manifold with a linkage to the carburetor.

Thus a 4GC is a four barrel, G type carburetor with automatic choke having the choke coil on the carburetor.

Of course these are not the numbers found on the tag or float bowl but are handy in finding the right part of the service manual and following what comes next.

Up through 1975 all factory Rochester carburetors were identified by a seven digit part number either stamped on a tag under one of the float bowl screws (1955-1965) or stamped into the side of the float bowl (1966-). The first two digits are 70 indicating Rochester Products.

By 1963 someone at GM got the bright idea of coding the nexttwo digits to the model year so 1963 became 23 and 1964 became 24. Thus a 1966 Carburetor p/n starts with 7026xxx.

Now this must have made too much sense so GM quickly found a way to foul it up: In 1966 California started requiring the infamous Air Injection Reactor or "air pump". These needed a different carb and to differentiate these from the normal sequence (7026xxx), these were labeled 7036xxx. For some unknown reason, '67 Ram Air GTOs and Firbirds also used 3: 7037271 (GTO) and 7037276 (Firebird). Thus when 1970 came along, instead of reusing 2x or 3x, Rochester jumped to 7040xxx which held until the 1976 digit increase (1975 was 7045xxx, 1976 was 17056xxx).

With the 1959 model year, the last three digits began to mean more than just a consecutive series. Numbering still began with 000 but decades were awarded to each engine manufacturer:

Chevrolet x0x x1x x2x
Cadillac x3x
Buick x4x
Oldsmobile x5x
Pontiac x6x x7x
Non-GM x8x
Special x9x

Thus a base 1963 389 automatic 2GC was p/n 7023060 and a 4GC for a 1966 Buick 401 was p/n 7026040. Note: this is true only for Rochester - Carter AFBs used a different numbering sequence.

In 1966 what had been a trend became a code as manual transmission cars were usually given odd numbers and automatic units became even numbered. Generally the most common engine/trans combinations were given the first numbers while odd-balls started higher. End carburetors in tripowers generally got x78 and x79 (Pontiac), 055, 056, & 057 (66 Oldsmobile), .

For many years, all numbering started with 0xx, but as carburetors proliferated 1xx started to be used for the overflow while keeping the same decade arrangement. For example 1964 421 tripower end carb is 7024079 while the slightly different 389 tripower end carb (smaller jet) is a 7024179. Type B or M one barrels, also were usually 1xx units though some (e.g. 1968 Pontiac 7028065 monojet, 1971 Vega 7041023) used the 0xx series.

The next change came with the introduction of the M type Quadrajet carburetor to Chevrolet in 1965, Pontiac on the OHC-6 and Oldsmobile in 1966, and across the board in 1967. Since a large proportion of Rochester's output was these, the QJ was assigned 2xx with otherwise the same assignment. Thus by 1967 another order had emerged not originally intended: 0xx were 2Gs, 1xx were mostly monojets, and 2xx were Quadrajets.

To confuse matters, with the 1969 model year, the 703xxxx designation for emissions carbs was dropped and California carbs began to use the following series when a special carburetor was fitted:

5th digit (series) 0 became 3 or 9
1 became 4 or 8
2 became 5 or 9

Thus a California QJet for 1970 400 B car automatic was a 7040562 while the Federal QJ was a 7040262. This numbering continued through 1975, however in 1970 the famous "corporate engine" mixing started and the number would carry the p/n of the parent factory. Thus if a 1972 Pontiac Ventura II used a Chevrolet 307 engine, the p/n would be 7042100 indicating Chevrolet.

Now you have a simple guide to breaking the code such as a 7041262:

70 - Rochester Products
41 - 1971
2 - Federal Quadrajet
6 - Pontiac
2 - base automatic.

There were no 350 four-barrels in 71, you can say "1971 49-state Pontiac 400 Automatic" and be 99% sure of being right.

One word of caution, Delco produces many service replacement carburetors each year. If you walk into a dealer and ask for a Quadrajet for a 1971 Toronado 455, what his book will show is a 17054934. The "1" prefix is a giveaway that something is not right (used after 1975). Be warned.

Rochester Carburetors were used on all standard performance Camaros. There are three types of identification on Rochester carbs. Models B, 2G, and 4G used a triangular metal tag installed beneath the air horn screw. The early Model M (Monojet) and 4M (Quadrajet) used a circular tag in a cavity in the side of the float bowl. Other carburetors used a stamping on the body of the carb.
The numbers include the model number, usually 7 digits, a change letter, signifying changes during the model year, and a date code (below)
The stamping or part number decodes as follows:

Example: #70 2 8 2 1 9 DG 1938

70 - Prefix code. "70" will appear on all late '60's Rochester Carburetors.
2 - Decade produced.
2 - 1960's
3 - 1060's with A.I.R.
4 - 1970-1975
5 - 1976-1979
8 - 1980's
8 - Year produced. 8=1968
2 - 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
1 - Division. 0, 1, and 2 all indicate Chevrolet.
9 - Transmission
Even numbers - Automatic Transmission
Odd numbers - Manual Transmission
DG - Customer code.
1938 - Date Code


Rochester Carburetors
Part
Number Carb
Model Year Engine Horse-
power Trans-
mission Notes
2 Barrel
702711 2GV 1967 327 210 ST
7027103 2GV 1967 327 210 ST A/C
7027110 2GV 1967 327 210 AT early
7027114 2GV 1967 327 210 AT late
7027116 2GV 1967 327 210 AT A/C
7028101 2GV 1968 327 210 ST
7028103 2GV 1968 327 210 ST A/C
7028110 2GV 1968 327 210 AT
7028112 2GV 1968 327 210 AT A/C
7029101 2GV 1969 307/327 200/210 ST
7029103 2GV 1969 307/327 200/210 ST A/C
7029110 2GV 1969 307/327 200/210 AT
7029112 2GV 1969 307/327 200/210 AT A/C
7029113 2GV 1969 350 250 ST
7029114 2GV 1969 350 250 AT
7029115 2GV 1969 350 250 ST A/C
729116 2GV 1969 350 250 AT A/C
7037101 2GV 1967 327 210 ST A.I.R.
7037103 2GV 1967 327 210 ST A.I.R. A/C
7037110 2GV 1967 327 210 AT A.I.R.
7037112 2GV 1967 327 210 AT A.I.R. A/C
4 Barrel
7027200 4MV 1967 396 325 AT early
7027201 4MV 1967 396 325 ST early
7027202 4MV 1967 327 275 AT 1st type
350 295
7027203 4MV 1967 327 275 ST 1st type
350 295
7027210 4MV 1967 396 325 AT late
7027211 4MV 1967 396 325 ST late
7027212 4MV 1967 327 275 AT 2nd type
350 295
7027213 4MV 1967 327 275 ST 2nd type
350 295
7027216 4MV 1967 396 325 AT 3rd type
7027218 4MV 1967 327 275 AT 3nd type
350 295
7028210 4MV 1968 396 375 AT
7028211 4MV 1968 396 375 ST
7028212 4MV 1968 327 275 AT
350 295
7028213 4MV 1968 327 275 ST
350 295
7028217 4MV 1968 396 350 ST
7028218 4MV 1968 396 350 AT
7029200 4MV 1969 396 325 AT
7029201 4MV 1969 396 325 ST
7029202 4MV 1969 350 255, 300 AT
7029203 4MV 1969 350 255, 300 ST
7029204 4MV 1969 396 350 AT
7029215 4MV 1969 396 350 ST
7037200 4MV 1967 396 325 AT A.I.R.
7037201 4MV 1967 396 325 ST A.I.R.
7037202 4MV 1967 327 275 AT 1st type A.I.R.
350 295
7037203 4MV 1967 327 275 ST 1st type A.I.R.
350 295
7037210 4MV 1967 396 325 AT late A.I.R.
7037211 4MV 1967 396 325 ST late A.I.R.
7037212 4MV 1967 327 275 ST 2nd type A.I.R.
350 295
7037213 4MV 1967 327 275 ST 2nd type A.I.R.
350 295
7037216 4MV 1967 396 325 AT 3rd type A.I.R.
7037218 4MV 1967 327 275 ST 3rd type A.I.R.
350 295



Carter-built Rochester Carburetors

Carter built Quadrajets for General Motors in the 1960's. All Carter-built carbs have "MFG by Carter" cast into the carb body. The carb number matches the Rochester number.
 
#8 ·
i actually believe the new truck avenger does better then my Q-jet did. my q-jet had problems starting when on a steep hill and the new holly fires right up. i have had my jeep on some very steep inclines. steep enough for my front tires to come of the ground and my ass hole puckker up, but the carb kept it all runing. it idles amazingly low, it will keep pulling and 300 rpm, and the side hill andgles are great, the downhill part is its only weekness, once it gets super steep, like, your tires dont stop you steep it chugs a little but never stalls. i love the carb and highly recomend it, scott
 
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