The Stovebolt Site Forums The Shop Area Engine Shop Carter YF 966S,

In my search for a Carter YF2100S carb, i ran across a YF966S, and bought it. After studying the info on the Carburetor Shop's site. It appears to me that the 2 carbs are very similar, but that the jets in the 966 are slightly larger, as is the metering rod. From that, my little pea brain is thinking that the 966S will probably not get quite as good fuel economy, but otherwise will very possibly suit me. My engine is a stock 235 from 1962. According to the same literature, the 966 was made for trucks from 50 to 52 with 235 engines. I assume that those were big trucks. While the 2100S was made for 235 engines from 53 to 59. Any info, tips, hints, etc. regarding this will be much appreciated by me.

The 50-52 235 would have been a dipper engine. That carb might have the smaller carb mount bolt spacing. Measure that. Otherwise, I don’t know why it wouldn’t work.

No, I checked that before I bought it. It has the larger spacing, and will mount on my manifold OK.

Run it. Have you rebuilt it yet?

I haven't rebuilt it yet. I just got it today. I'm looking forward to getting into it though.

https://www.stovebolt.com/ubbthreads/ubbthreads.php/ubb/showflat/Number/1181544

My YF 966S spec sheet says:
Chevrolet Power Glide and Truck 1950-52 for 3-9/16 bore, 3-15/16 stroke.

Chevrolet lost sanity in 1950 and switched from Carter to Rochester.
The YF-966S is a replacement carburetor for the 235.

My YF 2100S spec sheet says:
Chevrolet Truck 1953-56 for 3-9/16 bore, 3-15/16 stroke.

The YF-2100S is a replacement carburetor for the 235.

The question I would like to have answered is, if I had a choice of either, which one would work better on my 261?


[i][/i]

The major difference from the 966s to the 2100s was Carter found the idle circuit on the 966s to be slightly rich for the 235; and leaned it for the 2100s.

Both have a 1 5/16 inch (33.3 mm) venturi, which is slightly smaller than the venturi GMC used on the Zenith carb for the 270 (34 mm).

I would guess the 966s would be a somewhat better choice for the 261 because of the richer idle circuit.

Please understand the above is a GUESS based on statistical data; I have not personally tried this conversion.

Jon

I run a 966s on my 1957 235 in my 1950 3100.
Best switch I have done.
It runs , idles, like a dream...
I had a Rochester originally which ran not so well and leaked on and off.
-T

I don't think Chevrolet lost sanity...I think some GM exec had a son or grandson who failed out of engineering school and needed a job.

Actually, Rochester was a Division of GM. GM made more money by using in-house parts rather than buying parts. As some wise person once said "Follow the money!".

But if one looks at the model production history of Rochester:

1949 - first carburetor, model AA used on Oldsmobile (Rochester took a trick from Stromberg, the double letter meant 2-barrel)
1950 - revised model AA used on Oldsmobile, and model B (single letter, single barrel) introduced on Chevrolet
1951 - model AA discontinued forever (thankfully!)
1951 - model BB (double letter, two barrel) introduced on Oldsmobile and Cadillac
1952 - model BB discontinued forever (thankfully)
1952 - model 4G introduced on a number of vehicles (GGGG would have been awkward, so terminology was changed to 4G, just as Stromberg used the 4A).
1955 - model 2G introduced on a number of vehicles.
1965 - model M (4MV) introduced on Chevrolet
1968 - model M (MV single barrel) introduced

So summarizing:

There was no single barrel version of the model A
The two barrel version of the model B was discontinued after 1 year

The model 2G was used from 1955 through at least 1974 (the latest information in my database)
The model 4G was used from 1952 through 1966
The model B was used from 1950 through 1968, but the two barrel B was discontinued after 1 year

WHY was there no single barrel model G?

Jon

Just some thoughts.

The internal parts of a PowerGlide robs a % of HP to the rear wheels so Carter richened the idle circuit and metering to compensate?

Comparing (on paper) the main jet & metering rod:
YF 2100S versus YF 966S (jet area minus rod area times 100,000)
Main jet 0.0945"....0.1015"
Economy 0.067"....0.073" (356....399)
Midrange 0.060"....0.059" (426....544)
Power 0.050"....0.050" (512....621)

Using Ethanol gas, the YF-966S could be the better choice for a 235.

I ran a 966s on my 56 235 for a few years. I finally found a 2100s and switched over. I didn't notice much of a mpg difference since these trucks don't get very good mileage anyway especially with today's gasoline.

Was there much difference in the way it ran?

Not noticeable. I had some hard starts when it was warm. But I had the float out of adjustment. I still have the 966s as a backup carburetor. It's a good carb if you can't find a 2100s. Just my opinion.