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Author Topic: Rochester carb application  (Read 3308 times)
dab67
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« on: March 06, 2008, 05:07:15 PM »

Once again I need the expertise of CRG.

Can someone tell me the differences between a 4 barrel Rochester Quadrjet that is used by Chevorlet against one that is used by Buick or Olds considering they were all being used on small block V8's. Were there that many difference for these carbs? Did it make a big difference if the car had an auto or stick tranny? I'm talking about Quadrajets used lets say between 67 and 70 or 71 by all three manufacturers. My though process goes something like this, Rochester shipped x number of 4 barrel carbs to each facillity and based on the application of the manufacturer(example 1969 350 auto tranny) determined what id tag was attached to the carbs to show the application. Or is this thought process way out of wack?HuhHuhHuhHuh? Huh Embarrassed  The reason I ask, I've been told that the internal parts like the jets and such were different.

Thanks!!!!!!!!!!!
dab67

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hotrod68
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« Reply #1 on: March 06, 2008, 11:01:51 PM »

The Quadrajunks were jetted differently for a certain application--i.e., one for a 455 Olds 442 would be richer than one for a 327/250--the secondaries would be calibrated to open at a different vacuum, etc... Actually, the Junks used metering rods instead of jets, unlike a Holley, which was used pretty much only on performance engines. As to how GM determined their usage I have no idea. But it makes sense to me that mass-production would demand they be as generic as possible, as you allude to. Somebody on here will know. Hope this helps in some way and good luck! I'm now as curious as you about how the I.D. tag was determined.
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HotRod'68  1968 SS350 coupe undergoing frame-off resto/rod. 386/350/4.11s
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KurtS
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« Reply #2 on: March 07, 2008, 01:39:36 AM »

I'm not quite sure of the question. But each part # was unique and would have unique components and calibration. The part # was then stamped on the carb.

They were not generic at all. They were tweaking the carbs to pass the emissions test, hence the number of models.
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Kurt S
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opelitis1
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« Reply #3 on: March 07, 2008, 07:47:00 AM »

Just checked a couple of Q-jets from the 60's and there is a circle with (7)raised numbers in it on the rear of the throttle body close to where the H A C  would reside.  Numbers are not the same as the vertical 7 numerical identification stamping.  I took the top off the carb and turned it over and there is another one of these id circles with (7)raised numbers... 
I wonder if Camaro had a unique carb body to it and Corvette's had their own distinctive carb body easily identified with the different numbers within the "ID" circles.
I am not referring to the round metal data disc on the driver's side of the unit found on the 66 and 67 carbs.
How might a Corvette conaisseur spot a Vette carb in lieu of a Camaro/Chevelle unit???
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JohnZ
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« Reply #4 on: March 07, 2008, 11:29:15 AM »

How might a Corvette conaisseur spot a Vette carb in lieu of a Camaro/Chevelle unit???

All Q-Jets were identified by the 7-digit part number stamped on them, sometimes followed by a 2-digit alpha broadcast/usage code. Corvettes didn't use Q-Jets until 1968, when the different applications used 7028207, 7028208, 7028219, 7028209, and 7028216. In 1969, Corvettes used 7029203, 7029202, 7029207, 7029215, and 7029204.

Although the main body castings were similar, each part number of carb was individually calibrated for a particular car/engine/transmission combination for emissions compliance.
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'69 Z/28
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opelitis1
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« Reply #5 on: March 07, 2008, 01:34:04 PM »

Hi John Z!!!  On the rear of the main body casting, there is a circle with 7 raised  numbers that are not the same as the  7 digit part number that you are referring to above..  I just got up from the basement and wouldn't you believe it, the carbs I was after were on the bottom of my Rochester carbs but in a thickly designed box...

Here we go: 1 st carb 29202 DH dated 086 9 with raised numerics 7037931 in circle near where HAC screw holes are... Inverted air horn and encircled numbers 7307703
                  2 nd carb 29202 DH dated 098 9 with same as above 7037931 numerics.
Did not take the air horn from the 2nd carb but, it is possible it is the same ....

Looks like Rochester / GM had a certain number of carb bodies by the number 7037931
and even though these carbs are 12 days apart, they used the same 7037931 for both
units...  Did not check the rods / hangers / jets as they might have been changed in over 39 years at one time or another... 

Started a thread on the 6th in the De-coding/Numbers section of this board , but as of yet no responders...  Was there ever a list of carb bodies that was peculiar to Corvettes and not Camaros/Chevelles/ChevII but used the same 29202.
Do judges go so far as to check the encircled numbers or do they just look for the 7 or 5 numbers that are easy to read on the side of the carb...
Sorry to be so long-winded, but you dah man!!!  Ted
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dab67
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« Reply #6 on: March 07, 2008, 05:48:41 PM »

How might a Corvette conaisseur spot a Vette carb in lieu of a Camaro/Chevelle unit???

All Q-Jets were identified by the 7-digit part number stamped on them, sometimes followed by a 2-digit alpha broadcast/usage code. Corvettes didn't use Q-Jets until 1968, when the different applications used 7028207, 7028208, 7028219, 7028209, and 7028216. In 1969, Corvettes used 7029203, 7029202, 7029207, 7029215, and 7029204.

Although the main body castings were similar, each part number of carb was individually calibrated for a particular car/engine/transmission combination for emissions compliance.

John Z:  could a carb that was setup for a Pontiac 4 bbl be used on a Chevy or Olds by changing the jet settings and rod settings? could a big block carb be used on a sb?

dab67
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JohnZ
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« Reply #7 on: March 08, 2008, 11:11:36 AM »

John Z:  could a carb that was setup for a Pontiac 4 bbl be used on a Chevy or Olds by changing the jet settings and rod settings? could a big block carb be used on a sb?

dab67

I'll defer to someone who knows more about Q-Jets than I do - I've never had one - all my cars have had Holleys.
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'69 Z/28
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colinb67
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« Reply #8 on: March 08, 2008, 02:01:33 PM »

Do me a favor and double check that Q-jet stamp number. I'm CARQUEST parts store Mgr and checked the Standard carb kit book. The  numbers in the book skip over the number you posted. The number that will determine what those Q-jets fit is on the drivers side, by the throttle, on the side of the secondary casting. I'll try to help.
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Colin B. 1967 SS clone, 1993 Z-28.
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