2100s was for the 235 (1953 to 1956). Also on 235 were 788s, 789s, 966s, 967s, 2101s and 3211s. There were a couple of numbers in the 800 number series reserved but there was no production (890s and 891s)
If a mechanic and carb rebuilder told you that, they might be confused. No, I would not look for a Rochester to replace it. The 2100s was a good carburetor.
If you want to clean and rebuild it and check to see what you have in there at the same time, here is the Carter data and notes I have:
float setting: (with no gasket but with float resting on seated needle) 9/32" drop: 1 1/4" adj by bending stop tabs on float arm
vents: outside, no. 12 (.189 inch) drill, inside balance vent size, no. 42 (.0935 inch) drill in air horn
gasoline intake: spring loaded needle, size no 46 (.081 inch) drill in needle seat.
Low speed jet tube: size no. 70 (.028 inch) drill. Bypass in body, size .069 inch diameter. Economizer, size no 53 (.0595 inch) drill
Idle port: upper port, slot type, length .190 inch width .040 inch.
idle port opening: top of port .143 to .147 inch above top edge of valve with valve tightly closed.
lower port (for idle adjustment screw): .0615 to .0655 inch diameter
set idle adj screw: 1 to 2 turns open. For richer mixture, turn screw out. Do not idle below 425 rpm. Powerglide at 475 rpm
Main nozzle is installed permanently. DO NOT REMOVE drilled passage is size no 59 (.041 inch drill)
Metering rod: economy step .067 inch diameter, middle step tapers to .060 inch power step is .050 inch diameter.
Metering rod jet: .0945 inch diameter
Metering rod setting: see company instructions/adjustments
Accelerating pump: diaphragm type, vacuum and mechanically operated. Pump jet size 74 (.0225 inch drill) intake ball check seat size no 40 (.098 inch drill), discharge needle seat (in body) size no 42 (.0935 inch drill), vacuum restriction in flange size no 55 (.052 inch drill), vacuum passage (diaphragm bleed) size 56 (.0465 inch drill) and pump bleed into bowl size no 75 (.021 inch drill).
Pump adjustment: see company instructions/adjustments should be adjusted anytime the carburetor is reassembled.
Choke: manual
vacuum spark port: horizontal slot type, size .125 by .040 inch. Top of port (early prod) .030 to .040 inch and (late prod) .035 to .045 inch above top edge of valve with valve tightly closed.
Good luck, hope it helps.
