Carter AFB 3721S application

[Joseph R.]

Can anyone identify the probable original application of this Carter AFB carburetor? As you can see from the photos, it is stamped 3721S low on the casting but there is no apparent stamped date code. It has a six mounting hole body with casting number 0-1552 as best I can read. The upper tubes appear to be brass.

This carburetor sits on a block stamped F0103RD which appears to be right for the E9 build date code on the trim plate of this 1964 Corvette. I noticed the kink in the choke plate linkage which appears to be a non-standard for Corvettes. The accelerator pump linkage does not have a kink - is it possible to mistakenly swap these linkages on reassembly? As the photos show, the top of this carb was removed at some point as there are many screws missing there and the tag is gone.

I saw a question posed but not answered in the archives about the straight (or not) linkage so maybe that is a clue to the original application. My understanding is that the likely original Carter AFB on an RD motor assembled in January 1964 would be 3721SA and it would be date stamped.

So what was the likely original application of a 3721S carburetor stamped in this manner without a date code? Could this 3721S be set up to perform the same as an 3721SA or SB (is the difference just a question of jetting and swapable internals?) Thanks for your help, Joe

[Timothy B.]

Re: Carter AFB 3721S application

Joseph,

I can tell you that the early 64 RD (300hp) engines used the 3461S inventory before switching to the 3721S Carter. So IMO, I think it's probably correct for the E (January) build date on this 64 Corvette you are referencing.

The differences in the Carters would be calibration, (jets, metering rods, air bleeds, etc.)

[Joseph R.]

Re: Carter AFB 3721S application

Timothy, thanks for the information. Are there other examples of legitimate, originally-installed 1964 Corvette Carter carburetors not having a stamped date code? Or did other GM divisions not require date stamping on the mounting flange? And are there other ways to define the manufacture date of these Carter AFB carburetors? Would the model number and date code have been gang stamped all at once?


I did see in The Complete Corvette Restoration and Technical Guide, Vol.2, Second Edition on Page 225 regarding the L75 engine that "In spite of the October 1963 changeover date, three 1964 Corvettes included in our survey reported the 3651761 carburetor." That October changeover is the switch from 3461S to 3721S you mentioned, with the 3651761 GM part number being the Carter AFB 3721S according to The Guide. I think from context that sentence from the guide meant to reference the earlier 3826004/3461S carb, as the provided abbreviated survey list on page 225 doesn't support the text. And there is a mysterious entry in the Supplemental Data on page 252 of The Guide regarding a carb mounted on a L93 date code manifold (about the same time mine was cast) and "3721S AFB,DTEM3". The seemingly random application of SA,SB and S carbs over time indicated in that 1964 survey table is surprising.


So that is why I'm confused and wondering if the kink in the choke linkage is a clue about my carb's original application. I think the original S setup would perform fine on this L75 engine near sea level. Thanks, Joe

[Timothy B.]

Re: Carter AFB 3721S application

Joe,

The Carter AFB's used in order are 3721S, 3721SA and 3721SB starting in 1964. The carburetor you have will work fine on your L-75 engine. The choke linkage abortion shown in your picture is someone's attempt to adjust the fast idle, it's easily corrected with a replacement rod.

This carburetor is the correct part for your car so if it's linkage and throttle blades are free you will be surprised how good a rebuilder will make that carburetor work. It's also important to check that someone has not tightened the emulsion screws to tight and punched out the area around the carburetor base.

As far as the date code, the 3721S is stamped low on this carburetor boss so the date stamp just missed the carburetor. I know for a fact the date stamp is stamped below the 3721S stamp so you can see what I am talking about. This carburetor is also used on the Chevrolet SS models with the 300 hp engine but once again, it's the correct part for your engine.