The Stovebolt Site Forums The Shop Area Engine Shop Rochester carb observation

All,

While doing some research on a non-original motor in a C50 grain truck I picked up last year, I have made the following observation. A lot of "technical" information is just copied from one website to another and then claim themselves to be the authority, etc.

Well, I visited just about every Rochester carb ID site and all of them tell me same thing and that the fourth number on my carb, which is a 9 is for 1969. They also say the four digit date code is the Julian date and year. Mine is stamped 3477, which would make it Dec 13th, 1967.

According to everything I read on the innerweb, the fourth number of the carb number and the last number of the date stamp would have to be the same number!

Hmmmm, is my carb a 67' or 69'

So, don't believe everything you read.......

Just sayin,

BaconFarms

Lots of pixels have been unnecessarily disturbed on the internet for many reasons, this being one of them!

Since you did not post the URL's you mention, I have no idea what you read, HOWEVER:

I started telling customers about the Rochester identification GUIDE some 35 plus years ago, but it is just that, a GUIDE. And I have always told those who listened that it was just a guide. Probably 95 percent of the time, the GUIDE would be correct (which means 5 percent of the time it is wrong!).

Some examples:

(1) 4th digit same as production year - wrong! The 4th digit is GENERALLY the same as the production year carb went in service.
7028273 - production year 1968 - FIRST production year was 1968, but held over through 1969

Also, certain carbs were designated "service replacement units", thus they could be built long after the production year. In the "numbers-matching" world, service dated carbs generally are valued at less than 1/2 of original dated carbs. Also, with a few exceptions (generally those produced in 1969), the service dated carbs will not have "picking" codes.

(2) last digit odd is manual transmission - not always.
7028235 - odd last digit, Carb was original on a 1968 Cadillac El Dorado (when was the last time you saw a '68 Eldo with a manual transmission?????)

(3) date code was in the format jjjy (3 digits Julian date, 1 digit last digit of year) - YES, beginning on some (not all) models in 1968. Prior to 1969, the date code was 2 character in the format "my" where the "m" was a letter representing month (A=January, B=February), etc; and the "y" was the last digit in the year; HOWEVER: in some years the "I" was used, so "L" would represent December, and in other years, the "I" was not used, meaning "M" would represent December

(4) There are other discrepencies, but these should be sufficient to prove the GUIDE is NOT 100 percent.

Use it as a GUIDE, and it can serve you well, but if you have to be certain, look up the exact number.

Jon.

Mix and match from different carbs at some point in it's past.

And I mentioned the "picking code" (a.k.a. "plant code") in the previous post, so will elaborate.

Some of the assembly line workers had to quit school at an early age to support their families, so the 7 digit (later 8 digit) identification number WAS NOT USED when building the engine. The engine came down the assembly line with a "build sheet". The build sheet was a piece of paper, generally with a number of boxes, some of which contained a 2 character code - the "picking" or "plant" code. The worker would look at the build sheet in the box for "carburetor" or "distributor" or whatever and see two letters. These same two letters would be boldly placed on a large bin containing, in this case, a carburetor. As a cross check, either the letters, or the bin would be painted a specific color. There would be a splash of this color on the carburetor. Carburetor tags started about 1959 were color-coded. Of course, the first time the tag goes into the cleaning chemical, the color is removed from the tag. Later carbs, beginning on some but not all models in 1968, has a color-coded paper tag with the last 3 digits of the identification number and the picking code glued onto the body of the carburetor. Again, the first dunk in the junk and this tag was history. Please note that the term "plant code" did NOT refer to a specific plant, rather to an internal code used by the assembly plants.

And that is enough typing to last me the rest of the day

Jon.

Jon, some of our drive-by shooters with a low post count seem to prove the adage (repeatedly) that "A little knowledge is a dangerous thing!"
Jerry

Jerry - I believe what is more dangerous is the mistaken belief by many that whatever may be posted on the internet is true. The OP did notice that many sites seem to be "parroted" (we used to call it plagiarism) from one to another, and that the information was not necessarily true.

Seems some of the younger enthusiasts, that have grown up with the internet do not realize that there is a huge amount of data (called books) that is not now, and maybe never will be, posted to the internet.

As an example, my library of carburetor books takes up more than 250 linear feet of shelf space. Plus hundreds of rolls of microfilm, thousands of individual slides and aperture cards, a very large blueprint cabinet full of blueprints and drawings, etc.

Way less than 1 percent of this is posted, and may never be posted.

We old geezers have to help the youngsters learn how to find that which is not on the internet.

As far as the data on the internet, I have said since I first signed up that there is good news and bad news about the internet.

The good news is that anyone can post!

The bad news is that anyone can post!

I think the OP had the right idea; he found something amiss, and came here to ask about it.

Jon.

Jon,

Thank you for the education.

I know this is an old truck site, but I didn't want to start being a member of a bunch of chevelle or camaro sites, just to see what I have in my '70 C50 grain truck. I know the motor, heads, intake are 1972 BBC chevelle camaro chevrolet by their numbers, but like you said, the carbs were different.

With that said, all of the sites I went to had the exact same info on carb de-coding for the Rochester. They were absolute and offered no exception. Which I obviously have with the numbers on my carb.

It was mostly for discussion, as I determined that the carb was not part of the original package, which I was hoping for, for when I part with it.

Site rocks,

BaconFarms