Howdy All:
FYI- "Motorcraft" is a johnny-come-lately name for the Autolite 2100 series of two barrel carb. It appeared in 1975 and remained until the end of of carburetors in the mid 80's. They are "2150" rather then 2100s. Motorcraft 2150s would not be my first choice when looking for an Autolite two barrel to adapt to a Ford six. While similar in appearance and function they have several features that complicate them and make them less inviting for adaptions to engines other than the engine they were designed for. To name a few of the features; variable air bleeds, egr ports, and sealed bowl vents. They became more encumbered with enviromental crutches as the years went by. The 2150s do have annular discharge venturi boosters and are of the same simple, sturdy design as the 2100. They are a good source for jets and for electric chokes.
All Autolite carbs from 1959 on will have the venturi inner diameter cast with raised numbers in a dime sized circle on the side of the float bowl, under the accelerator rod. This number equates to the CFM rating for that carb. For instance a carb with a 1.02 casting identifies this carb to have a 240 CFM rating.
You will notice that three pairs of carbs sizes exist. They are 1.02 (245 cfm) and 1.01 (240), 1.14 (300 CFM) & 1.08 (287), and 1.23 (356 CFM)& 1.21 (321cfm). In each case the second number carb appeared later in the model year run for that engine, most in '68 to '70 years. It is my supposition that Autolite did this slight down size it increase fleet MPG ratings and to lean out the emmissions. While 5 to 25 CFM less may not be noticeable in most situations, a leaner choke and idle circuit could be. All things being equal our sixes seem to like a richer idle. Personally, I prefer the Pre '68 versions of the 2100 for adapting to our sixes.
Q- "which autolite 2100 would work great for my 250ci engine?"
A- A 1.02 or 1.01 (260 V8) from '63 or '64, a 1.14 or 1.08 (289 and 302 V8) from '64 - '74 would all work on a stock or lightly modified 250 street engine.
Q- "what are great 1 bbl carbs?"
A- There are only three "Good" choices for a Ford 250. They are an Autolite 1101 (210 CFM) from a '69 250 Mustang, a Carter RBS (215 CFM) used on 250s from '70 to '74(?) And Carter YFs (?CFM) used on early 300 six pickup engines. All three are fairly simple, straight forward carbs that can be tuned to be very streetable and to perform well.
Keep us posted on your choice and your progress.
Adios, David
