Rochester Quadrajet carburetors: Identification and decoding
From Crankshaft Coalition Wiki
 Identification Number Location
- The number is usually found either as a tag or as a stamping in the body on the driver-side of the carburetor, running vertically up and down. ^1
 Identification Number Decoding
- It is not uncommon for confusion to arise when decoding a Quadrajet carburetor. According to Recarbo Fuel Systems:
"This guide is just that: a guide. It is not set in stone, because it is a documented fact that Rochester didn't follow these rules 100%. It is for Quadra-jet carburetors only. Rochester also had different numbering systems for their other carbs besides the Quadra-jet. Our thousands of pages of information on this comes straight from Rochester.
Keep in mind that just because the OEM numbers between two carbs may be different, it doesn't mean they are different carbs. It's very possible to have two carbs, their date is 2 years apart, one is for Buick and one is for Chevy Truck, and one is for automatic, the other for stick, and the carbs are identical in every single way, even down to the jets and metering rods. It's much more common than you might think. Also, many people think they have to have a carburetor with a certain exact OEM number. This can sometimes be very very hard. Most people don't have to have this, they really only need a carburetor that crosses over the same and is identical. You realistically only need an exact OEM number if you are restoring a car back to original condition to enter into a car show."^1
- Using the ID number from the image above, here is an example of the breakdown of these identifiers:
- 17052575 APP 3356
- 170 – Built: 1975 and onward by the Rochester Division of GM
- 5 – Decade produced: 1976 - 1979
- 7 – Year produced: 1977
- 5 – Model: Quadrajet (4bbl) California Standards
- 2 – Division: Chevrolet
- 5 – Transmission: manual (this particular carburetor was found in a 1977 Chevy truck with an automatic transmission)
- APP - Plant code
- 3356 - Build date code: 335 day of 1976
 Online Sources for Identification and Decoding
- Carburetor Designation/Identification - Covers casting designations and identification numbers. From Cliff Ruggles' Cliff's High Performance.
- Recarbo Fuel Systems - "This guide is just that: a guide. It is not set in stone, because it is a documented fact that Rochester didn't follow these rules 100%."