Rochester quadrajet markings 1965-1974

Note that this information covers the years 1965 – 1974. As we do not work on the newer carbs, we do not have sufficient books or experience to comment on the newer units.

There are many codes (both letters and numbers) found on the Rochester quadrajet.

Without getting into the actual numbers and letters, this article is an attempt to delineate the meanings of some of the codes.

The three main items, which seem to be of interest, are: (A) part number; (B) date code, and (C) plant code.

The part number will be stamped on a round tag pressed into the driver’s side of the bowl (center section) of all original 1965 – 1967 quadrajets; as well as some very early production original 1968 quadrajets. The part number will be stamped vertically on the driver’s side of the bowl (center section) in the area of the secondary on later production original 1968 quadrajets; all 1969 - 1974 quadrajets; and service dated replacement 1965 – 1967 quadrajets. Part numbers stamped in 1968 MAY not be uniform in striking density, size, height, or even font. Part numbers were meant to be a 7 digit number beginning with a “70” during this time period. Often, especially in the years 1968 and 1969 the “70” are omitted, and a 5 digit part number will result. When confronted with the 5 digit number, simply concatenate the “70” to the front of the 5 digit number again making a seven digit number. Do not confuse the 5-digit number with a possible 5-character number (4 digits and the letter “S” as in Sam). Carter produced millions of quadrajets with original numbers for original applications under license from GM. Carter ALSO produced retail aftermarket carburetors (with O.E. calibrations) under the Carter numbering system, which is 4 digits followed by the letter “S”. These will only appear on those carburetors, which are marked Carter.

The date code may be in a number of areas. Those carburetors that were originally tagged (see above paragraph) will have a 2-character date code stamped into the tag. Most 1968 and some very early production 1969 original carburetors will have a 4-digit date code stamped on the drivers' side of the throttle body (lower casting) just to the front of the rear mounting hole. Later 1969 quadrajets through 1974 will have the date code (either a 2-character code if produced by Carter, or a 4-digit code if produced by Rochester) stamped on the driver’s side of the bowl (center section) in front of, behind, or under the part number. The 2-character codes will be in the format “my” where “m” is a letter designating the month of production (A=January, B=February, etc.), and the “y” is the last digit in the year. Example A9 would represent January 1969. The 4-digit code is in the format “jjjy” where the “jjj” is the Julian (sequential number) day of the year and the “y” is the last digit in the year. Example 1 – 0018 is January 1 1968 (001 the first day of the year). Example 2 – 3668 is December 31 1968 (366 the last day of a “leap” year).

The plant code is the most misunderstood of all. This code is NOT; repeat NOT the code for the plant producing the carburetor. The plant code is the code that was used by employees at each plant INSTEAD of the 7-digit part number. This plant code is similar in nature to the 2-character engine code, which is stamped on the front of the engine. These codes were used to minimize errors. The broadcast or build sheet that would accompany the engine down the assembly line would contain these various plant codes for a number of different accessories, including the carburetor. Each individual number carburetor will have a corresponding and unique (for that year) plant code. The plant code would be stamped on the tag of tagged original carburetors (see part number paragraph). On ORIGINAL carburetors with the stamped number on the bowl, the plant code will be stamped on the same pad as the part number. Most (not all) service dated replacement carburetors were not stamped with the plant code. One notable exception is 7037262 that seem to have plant codes even on much later dated carbs.

Other numbers. Most of the castings will have RAISED 7 digit numbers, often in a small circle. These are BLANK CASTING numbers. This means an internal (to Rochester) number for an unmachined “blank” casting. The castings could then be machined a number of different ways producing different (and thus NOT interchangeable) parts. An example would be the very few quadrajets, which used no primary metering rods; thus the vacuum passage beneath the power piston assembly would not be drilled.

Stamped numbers on castings. Some castings will have a 4 or 5-digit stamped number which is an internal code specifying how the casting was machined (see previous paragraph) thus interchangeability. Some castings will have a 3-character code, which often represents a “clock” or “shift” code.

5-digit stamped numbers on parts, such as the air valve shaft or air valve butterfly plates. This number often (and just as often not) refers to the last five digits of the Rochester part number for this part. If the part is a SINGLE part i.e. the butterfly plate, then the 5-digit code is PROBABLY the last five digits of the part number. If the part were an ASSEMBLY i.e. the air valve shaft (composed of the shaft, the air, and the pin) then the number would represent the last 5 digits in the internal part number for that component, but not the assembly.

One other comment on markings: ALL of the tags (1965-early 1968) are color-coded. This color code was another check used by the assembly plants to minimize mistakes. The tag was anodized aluminum, not paint. I also will not publish the table of colors. The newer stamped carburetors had a colored paper adhesive tag with the last three digits of the part number. Again, the color was used to minimize mistakes at the assembly plant.