Rochester Identification

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chromebumpers

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Rochester Identification

You can usually find the carbs casting number and date code on the driverside of the carb stamped vertically.

A typical stamping;
7045213 YA
101 5

70 = Rochester products division#
45 = Production year, 4=1970's, 5=specific year, 1975
2 = Carb ID, 2=49 state Q-jet
1 = Division, 1=Chevrolet products
3 = Tranny ID*, Even number=Automatic, Odd number=manual
101 5 = Julian Date Code, Friday April 11 1975
YA = Engine assembly plant

# Carbs starting with 70xxxxx are pre-1976. Carbs starting with 170xxxxx are 1976 onwards.
An important note: Primary metering rods are different lengths for the two units, both rods are available from GM, and the new-part part numbers correspond with the carb. Rods whose p/n starts with a 7xyz are for the 70xxxxx carbs, and p/n 17xyz are for the 170xxxxx carbs.

* tranny ID is not cast in stone. This particular example was original equipment on an automatic equipped pickup truck.



Production Year
15 = 1960
19 = 1961
20 = 1962
2x = 1963-1969
3x = 1966-1967 A.I.R. equipped vehicles
4x = 1970-1975
5x = 1976-1979
8x = 1980-?

x=last digit of model year


Carb ID
0 = 49 state mono-jet
1 = 49 state 2bbl
2 = 49 state Q-jet
3 = California mono-jet
4 = California 2bbl
5 = California and high altitude Q-jet


Product Division
0,1,2 = Chevrolet
3 = Cadilllac
4 = Buick
5 = Oldsmobile
6,7 = Pontiac
8 = Non-GM, possibly Mercruiser Marine
9 = Special


Julian Date Code
From our above example code;
101 = Day of the year (1 thru 364/5)
5 = Last digit of manufacturing year. (0 thru 9). Utilize carb id for 60's, 70's, or 80's.
Some of those multiyear calanders with a look-up table have the Julian day of the year on them. If not, you'll just need to count out the days.


Engine Assembly Plant
YA = ?
FJY =?



Examples
Our example carb, 7045213
Is a Rochester carb, for the 1975 model year, 49 state (federal) Q-jet, Chevrolet Division with supposedly a manual transmission.
What it was originally installed on was a non-emmisions controlled 1975 3/4 ton Chevrolet Pickup truck with a 350 cubic inch engine and an AUTOMATIC transmission.
How about another? 17083222
Date Code 0183
Is a 1983 model year, 49 state Q-jet, Chevrolet division with an automatic tranny.
Manufactured on the 18th day of the year, in a year ending in 3. For, January 18 1983
Originally installed on a 1983 1/2 ton Chevy Pickup with a 305 and automatic tranny.

And one more for fun, 7043114
A 1973, 49 state 2bbl , Chevrolet division, with an automatic tranny.
Originally installed on a 1973 Nova w/350 and automatic tranny.

 
From:

https://www.carburetor-parts.com/Rochester-2G-2GC-2GV-Technical_ep_288.html


2gc_identification.JPG




How to Find The Carburetor Number? The older Rochester 2G carburetors had a small triangular tag attached to the top of the carburetor. Starting in 1968 the 2G carburetor had the number stamped on the side of the float bowl below the inlet.

Pre 1968 2G carburetors cannot be identified without the tag. All other numbers found on these carburetors are casting numbers and part numbers that were used on multiple carburetor numbers.

Three Basic Types of Rochester 2 Jet 2G:
- Manual Choke 2GC
- Automatic Choke 2GV - Divorced Choke (choke thermostat is mounted in the intake manifold)

Tri-Power - The center carbs used on 1958 Cadillac, 1958 Chevrolet, 1957 and 1958 Oldsmobile, and 1957 and 1958 Pontiac used front fuel inlets.
 
 
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The second gasket set is for the large venturi Rochesters. It's missing a few key items, I guess it depends on how much you want to spend.
I have the instructions that show how to measure the float stops but it doesn't say what the measurements are, so where are they listed?
 
The Float Height & Float Drop settings are listed in Original GM Service manuals Richard.
Also in Vintage Mitchel - Chilton Sevice manuals.
GM Service manuals are most accurate .
I have a 1970 Pontiac Service manual & Mitchels & Chiltons 1959-73.
Will look up later tonight and let you know.
 
Try 9/16" Float Level.
1-3/4" Float Drop.
From my 1970 Pontiac Service Manual.
 
87vette81big said:
The Float Height & Float Drop settings are listed in Original GM Service manuals Richard.
Also in Vintage Mitchel - Chilton Sevice manuals.
GM Service manuals are most accurate .
I have a 1970 Pontiac Service manual & Mitchels & Chiltons 1959-73.
Will look up later tonight and let you know.
Click to expand...
Thanks Brian, I have those books actually and didn't look for such information, but since you noted they can be inaccurate I'll wait for your findings. If I couldn't find the measurements I would have tried just putting the float back in without touching the float tab.
 
UPDATE: I'm screwed now. The accelerator pump has a check ball at the base to allow fuel in and drop to stop flow. I used the new ball that came with the rebuild skit. I watched a YouTube rebuild that said to use the small ball, the one I put in wasn't the small ball. So I decided to change the ball and now it won't come out. Banging on the bottom, tapping from behind with a screwdriver and another screwdriver. Everything was very clean so cleaners won't work. This could be bad or it could be a good idea, I just put the carb body in the freezer at minus 8 degrees in the hope that the ball or the body will shrink. Meanwhile I guess I better start looking for a new carbureter.
 
Take A Heat Gun to the Carb body.
The wrong Pump discharge ball should fall out.
 
87vette81big said:
Take A Heat Gun to the Carb body.
The wrong Pump discharge ball should fall out.
Click to expand...
But that ball is wedged in there. Initially I dropped the ball down inside the the base of the accelerator and put in the spring that pushes against the accelerator pump assembly - so there was some force against that ball.
So Brian, you think heat will work under these circumstances? I sure hope so because now I've another car disabled in the garage and I can't have that happen. Time to pull it out of the deep freeze.
 
Ok deep freeze didn't work. I got out my professional heat gun and gradually heated after about 5 minutes under the highest setting I started tapping on the back side after a minute or so I beat on it a few times and it fell out.
Thank you Brian!

Now the hard part. I ran across a guy who claims to have 40 years experience with Rochester/QJets and he says there is supposed to be 2 check balls under the accelerator pump, my diagram shows only 1. I only removed 1 when I tore down this carb in the beginning. I need to know the correct size of these check balls. I have an aluminum check ball that measures 5/32" and a larger steel check ball that measures 3/16". The larger steel ball was the one that jammed.
Is this a common occurrence when buying rebuilding kits that you get main parts that don't match up or even work for the application?
 
I am at work in Chicago still Richard.
Use the Aluminium check ball.
Watch Grumpys You Tube Vids.
Check in later tonite .
 
87vette81big said:
Try 9/16" Float Level.
1-3/4" Float Drop.
From my 1970 Pontiac Service Manual.
Click to expand...
Are you sure about the float drop at 1 3/4"? It's at original setting of 1 1/4" right now. The float level was 9/16" so that remains unchanged. Dropping another 1/2" seems like a lot?
 
In the morning I will scan and post pages from my 1970 Pontiac Service Manual.

I took a look also in my 1965 Oldsmobile Service manual this morning .
Different specs listed for the 2GC.

Also have a 1963 Pontiac Service manuals I look at in the morning .

Pontiac V8 engines like lots of Gasoline fed to them WOT.
Much like a Big Block Chevy does.
 
Zxz
87vette81big said:
In the morning I will scan and post pages from my 1970 Pontiac Service Manual.

I took a look also in my 1965 Oldsmobile Service manual this morning .
Different specs listed for the 2GC.

Also have a 1963 Pontiac Service manuals I look at in the morning .

Pontiac V8 engines like lots of Gasoline fed to them WOT.
Much like a Big Block Chevy does.
Click to expand...

I have Motor Manuals from 1968 back to 1956 and I can see the 68 measurements are what you gave me but remember, my carb is 7043062 and that number is for a 1973 not 68. I don't yet have a 73 Motor Manual - one is coming this weekend, but for now is the float drop any different?
 
I just discovered I already have a Motor Manual for all models 1971 to 1977. The float measures have changed.
21/32 for float level and 1 9/32" for the drop.
Remember when I had a couple dozen QJets to dump, I wish I kept them now.
 
You wete in Clean up house mode last year.

The Pontiac V8 does more with less.
Torque Monsters .

Oldsmobile V8 is similar but with a slighly weaker power band.
I have found them more tolerant of todays shit pump gas.
Using factory iron heads and full ignition advance curves.

Big Block Chevy is an animal too.
Especially with Full Drag Race High compression Race Gas Fuel Fed Diet.
Spank a Hellcat Power.

All Rochester 2 G's are Very Similar.
The real difference is the Main Jetting used.
And the Removable Venturi Booster Cluster that has the Idle & High Speed Emulsion Tube Assembly.
Also the Float Settings used per application .

1970 Pontiac Carburator Settings have worked Excellent for me always .
 
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