1706 V-BCH Commodore
VB 17065008 - 5.0 T400
VB 17065987 - 5.0 T350
VC/H 17066297 - 4.2
VC/H 17066295 - 5.0
Rochester Numbering System
1949 - 1987
The Rochester Numbering system is not as easy to understand as some would like to make it appear. The "one-rule-fits-all" concept simply does not exist.
We need to understand that what we think of as the "Rochester numbering system" is in reality a "part numbering system"; and the part is simply the carburetor assembly.
Rochester did not leave us with a lot of records; at least not in one place. They made a product and updated their customers about that product; in this case the GM dealer network or others who either sold or repaired their carburetors. Many of those records have been lost, destroyed or simply thrown away. So what little information exists is difficult to find.
Rochester made carburetors to sell for new car production and service requirements.
They could not have known that 50 years later, we would want to document what they did.
Technical information related to performance or maintenance has been readily available for many years and there are several excellent books and websites that provide that information. There was very little, if anything, concerning the numbers; no one knew how to decipher them and Rochester didn't publish very much; and what was published was not what they consistently did. Although that did not deter enthusiasts from seeking any type of information about Rochesters, most authors of web-based information deciphered the numbers based on experiences and assumptions. Look at a carburetor; look at the car model, engine or transmission and publish some conclusions. Information about a few 1960's carburetors was generalized into "what has become FACT". This worked as well as it could and since it was all we had, and we did not know any different, we felt knowledgeable. By default, the information became our reality.
Leaving us with documentation likely never crossed their minds;
their intention was to “produce a product” and they made a lot of very good "product"!
After 5 years of research, specific information about the Rochester numbering system can finally be accurately discussed.
We’ll attempt to define the Rochester "carburetor assembly" numbering system, even though it was not ever clearly defined by Rochester. This “lack of clarity” was a contributing factor in the well intended attempts by others to “put something on the Internet”. Many even “inserted” a 1970 document from Rochester describing how the numbers were formatted; but this caused problems. No one could have known that Rochester published bulletins that were "year specific" and never told anyone that there was a difference in Original Equipment (OE) and Service carburetors numbering. This "generalizing" has left us with lots of "accepted truths" about Rochester carburetors. It's what MYTHS or made of . . .
Only after careful analysis of the factory application records can the “facts” be described in a concise manner. It will never be "not confusing" because everything Rochester did seems to cause confusion. They had exceptions to exceptions; many without explanation.
The following facts were derived from General Motors, United Service Products, Rochester Products, AC-Delco, Divisional Technical Service Bulletins and Internal Memorandums.
The following facts are known to apply to Rochester four-barrel carburetors and the production counts listed apply to these only; unless other carburetors are specifically mentioned. The analysis is still in process for the one- and two-barrel units. We will not make assumptions nor draw any conclusions until all of the data is analyzed.
This website will be updated as additional analysis is completed.
700xxxx
Beginning with the 1949 Oldsmobile, the Rochester one- and two-barrel carburetors utilized a seven-digit number that began with “700”. Although there are listings dating back to 1932, the first year of production was 1949. The listings for applications prior to the 1949 Oldsmobile are “generic” replacement carburetors. This “700” sequence was also applied to the four-barrel when the 4G carburetor was first introduced in 1952.
701xxxx
Beginning with a 1957 Buick, the number sequence evolved to the 701xxxx series. This continued through the entire 1961 production and all but a very few of the 1962 carburetors, at least for Original Equipment (OE) production. During this time, there was no defined digit to indicate the year of the carburetor or vehicle application. However, there are a large number of Service Replacement carburetors from the mid-1950‘s through the late-1960‘s that also use the sequence 701xxxx; beginning with a 1954 Cadillac and continuing through a 1969 Oldsmobile. Simply by looking at the carburetor or the number, it is virtually impossible except by an expert, to determine if a 701xxxx carburetor is an Original Equipment or a Service Replacement unit.
702yxxx
Well into 1962 production, the numbering system changed to the 702xxxx sequence. At least in theory, this was the first production year for a digit within the number to indicate the “year identification”. However, the reality is that very few of the ’62 carburetors denote the year with a 2 in the position indicated above with the y. As an example, there was only one 4-bbl carburetor with a 2 in the identifier position. That particular carburetor is 7022752 and it was installed on a 1962 Oldsmobile F-85 V8 MT/AT w/ or w/o AC, 3rd type.
The first 1962 carburetor documented with the year-identifying digit is 7022021, a 1-bbl installed on a GMC truck; however, for the entire 1962 production, there were only four carburetors, including the one 4-bbl, made with the 2 in the identifier position.
Contrary to what some Internet sites might state, the vast-majority of carburetors assigned to and designed for 1962 vehicles do not have the 702yxxx sequence. These all have the carry-over sequence from the 1950’s and early 1960’s. There was no explanation located in any Rochester documentation mentioning a reason for this.
The first full production year with a digit identifying the actual year of use was 1963. All 1963 Original Equipment carburetor production used the fourth or middle digit for the identifier (look at the y above). This year-identifier continued through 1974; at least for Original Equipment units. In this case, a “3” denotes 1963; a “4” denotes 1964; etc. The “702” sequence continued through the 1969 model year; however, with the evolution of the “emissions” carburetors, the “703” sequence began in 1966; therefore, Rochester used the “702” and “703” sequences concurrently. This concurrent use causes confusion in carburetor applications.
703yxxx
The “703” sequence, which began in 1966 and at least according to the “Myths” surrounding this number sequence, denotes carburetors designed for use on engines with emission controls. These are described with acronyms such as A.I.R. or C.C.C. This sequence used the fourth (middle) digit to denote the year like the “702” sequence, but the "703" series carburetors were only used as OE-production units for two years. There is no factory documentation indicating use in 1968 or 1969.Contrary to what some Internet sites might state, GM records indicate that the 703 series was only used for 1966 & 1967.
While 1966 is often referred to as the first year for emissions carburetors, the reality is that Rochester designed numerous carburetors with C.C.V. (Crank Case Ventilation) in the early 1960’s, which was an early form of emissions.
Although accepted as “fact”, it is a MYTH that the 703 series
carburetors were designed for emissions-only applications.
They actually have lots of other applications.
In some cases a “702” series carburetor was used for an application with emissions, even after the onset of the "703" sequence. As an example, 7027032 is a 4-bbl that was factory installed on a ’67 Oldsmobile with a 330 or 425 engine, with C.C.C. emissions.
In other cases, a “703” series carburetor was used for an application that did or did not have emissions. For example, 7037273 is a 4-bbl that was factory installed on a ’67 Firebird 400 with Ram Air and with or without California emissions.
But it gets more confusing. Rochester made thirty-six (36) Service Carburetors with the sequence designation “703” and the factory records reflect that only four (4) of those were made specifically to replace “emissions-specific” carburetors. The remaining thirty-two (32) were designed as replacements for “emissions” and “non-emissions” applications.
However, the confusion is not complete. The reality is that out of the total of 101 four-barrel carburetors documented with the 703xxxx sequence, 1/3 of them were Service Carburetors. Of the thirty-six (36) Service units, one (1) was designed as a replacement for a ’57 - ’58 Pontiac application and eight (8) were designed for 1970 applications. Interestingly, of the nine (9) that were not made for the ’66 - ’69 time period, all of those except two (2) were made specifically for Pontiac. Those two (2) were for Oldsmobile. Chevrolet and Buick did not use any of the "703" series service carburetors. (The 1-bbl and 2-bbl carburetors with the 703 sequence are not described in this section. They will be added when analysis is complete.)
704yxxx
Beginning in 1970, all Original Equipment Rochester carburetors began with “704” and this sequence lasted through the 1975 model year. This is a “time" that causes major problems with the fourth-digit “year indicator”. For all regular production carburetors, it is true that the fourth (middle) digit indicates the year; as indicated with the y in the number above. This remained constant through the 1975 year. According to Rochester’s published information, any carburetor with the 7041xxx number should be for a 1971 application. However, Rochester did not state all of the facts…
Service Replacement carburetors were produced in 1971 with apparently no “rhyme or reason” for a year indicator. There are twenty-eight (28) carburetors with the 7041xxx sequence that would appear to have been designed for 1971 applications; but only eleven (11) of them actually were! These twenty-eight (28) are within a sequence of carburetor numbers that are all Service Replacements. Eighteen (18) of these units were actually designed for many of the mid to late-60’s applications.
No documentation or explanations have been found, at least so far, that would explain the rationale for this numbering “exception”. Additionally, no Rochester documents have been located describing how to physically tell the difference between a 7041xxx, 1971 OE carburetor, and a 7041xxx, 1966 Service Carburetor.
1705yxxx
Beginning in 1976, the number increased to an eight-digit sequence, 1705yxxx, which lasted through the 1979 model year. With this new, expanded sequence the fifth digit denoted the year model. This stayed constant except for the Service Replacement carburetors (called “Service Carburetors” by Rochester). In theory, all 1979 carburetors should have this sequence, although there are numerous “late production” 1979 units with the numerical designation of a 1980 carburetor. Actually, many 1980 and some 1981 production cars have the 1979 sequence as they are “carry-over” carburetors. Just another element of confusion, compliments of Rochester!
This confusion was not unique. What might be the strangest documentation found is for a 1979 four barrel carburetor. One number (17059213) was built with two variations; a US version and a Canadian version. According to the factory records, they are very different. Rochester suggested the easiest way verify if a carburetor was the US or Canadian version was to use a truck service manual for comparison!
17080xxx | 17081xxx | 17082xxx | 17083xxx
Beginning with the 1980 model year, the designation for the year became very easy to determine; at least for Original Equipment carburetors. In addition, this is the first time in almost 30 years of production that Service Carburetor numbering was not confused with Original Equipment numbering.
In reality, only the fifth digit denoted the year, which was a carry-over from the late-1970’s; but the combined numbers are easy to see quickly and it’s simply easier to watch for those. By doing so, an “80” means 1980; “81” means 1981; etc. But, as with everything else Rochester or GM did to mystify these numbers, the 1980’s carburetors were not used in a way that simplified identification. In some ways, these are more confusing.
In the 1980‘s GM and Rochester took the “carry-over carburetor” to new heights. What apparently happened is simple in concept, but it really confuses anyone attempting to interpret a number. As an example, 1980 carburetors were often used on 1979 applications as well as 1980 - 83 applications, which is easy enough to understand. However, another 1980 carburetor might skip a year; it might be used on a 1980 application, skip 1982 and be used again in 1983.
The concept of “carry-over” carburetors was not new to the 1980’s. A “carry-over” simply meant that Rochester designed a carburetor for a specific year and it was used in other years also. There are hundreds of Rochester carburetors that were used for multiple years.
In a few cases, one model would have different emissions than another model; but they both used the same carburetor. As an example, 17080503 is a 1980 application for a 350 4v MT w/o AC Chevrolet Blazer / C10 pickup and a GMC Jimmy / C15 pickup. The Chevrolet models are California-only emissions and the GMC models are non-California emissions (49-state). This is only one in a sequence of truck carburetors that had very confusing emissions applications.
By the mid-1980’s, as GM and Rochester were preparing to phase out carburetors, a number might not be used at all during the year designated by the stamping, but would be used the following year.
What all of this means is that the year stamped into the carburetor during the 1980‘s meant it was used in “that year” - - unless it was used in another year - - which only adds confusion to this entire situation, compliments of Rochester and GM.
This sequence continued through the end of production.
701xxxx | 703xxxx | 704xxxx | 1706xxxx | 1707xxxx | 1711xxxx
Although these numbers might look the same as previously described, they are quite different.
These are Service Carburetor number sequences!
Service Carburetors are rarely described on the Internet and until recently, no documentation was provided about these units. While they do not have an actual year identifier, that does not mean they do not have a digit that appears to be a year identifier. Many of these contain a number that makes it appear to be an Original Equipment unit; notice the 701xxxx, 703xxxx, 704xxxx and 1705xxxx sequences previously discussed.
More Mystery:
Even though we now know many more details about the Rochester numbering series than ever before, there is still confusion; not to mention more questions than answers. As an example, within the 1707xxxx series of service carburetors, we know of entire sequences for which no documentation has been located. These have been reported to CarburetorData.com by readers who are asking about their carburetor and why their carburetor is not contained in The Guide.
Some of those reported to us are 17070839 and 7047687; or even more interesting is 17077769 and 17077522.
The first two numbers are reportedly two different carburetors. Without photos of the various numbers, it is impossible to identify these with any certainty or to say if they are carburetor assembly numbers or carburetor bowl part numbers.
However, 17077769 and 17077522 are two numbers on the same carburetor. Again, without photos, it is impossible to say anything definitive without a large amount of speculation. At this time, the only information we know is we have several numbers that are "unknowns".
My uneducated appraisel would be
17069595 :- "PROBABLY" A POST - a 1976 to 1979 "style" carburettor
1706
9595 :- a 1979 or last of the iterations of this style of carburettor or a carry-over carburettor used in other applications extending past the initial date range.
17069
595 :- California Emissions standard.
170695
95 :- division (Australia) used from (HT) on.
1706959
5 :- Transmission Even # Auto / odd # manual
SO STATESMAN CARBY - "POSSIBLY"
Edited by user Saturday, 7 July 2018 1:21:24 PM(UTC)
| Reason: Not specified
