Is this true:

"In the classic car and tuning community, 3-step rods are generally treated as an unwanted restriction. They make tuning a carburetor incredibly difficult because you have to balance three separate fuel curves instead of two. Unless a vehicle must pass a strict vintage emissions inspection that requires factory-original parts, standard practice across enthusiast communities is to swap the tall jets and 3-step rods out completely. Replacing them with a standard 120-series short jet and a standard 75-series 2-step rod delivers immediate, predictable throttle response, better mid-range power, and makes the carburetor infinitely easier to tune."

I've got a few old BBD's, they all seem to have 3-step rods and the taller jets (I think they're taller because they have a guide hole at the top that is technically not the actual jet). I recently picked up a china clone BBD (not the solid-fuel tin-top type, but the older type) and these also have a taller jet and 3-step rods. I measured the jet and rods and tried to find any talk or mention on-line of comparable sizes to see if my sizes are correct or match what was used in actual carbs, but I really can't find much in the way of tables or charts on 3-step rods or jets. The above AI quote, if true, indicates that these 3-step rods/jets were tossed and replaced with 2-step alternatives, seemingly the only real difference was the 3-step had a leaner setting for cruise? That actually does appeal to me.

But anyways, is there an on-line chart or table somewhere of typical 3-step sizes? (this is for the 1.25 inch BBD).

Bonus question: What are my best 2 and 3 step options for running E10 gas? (if indeed anyone has ever worked that out)

Where did you see this? It reads to me like "AI" slop from the likes of ChatGPT.

No, you don't get better throttle response or shinier dishes or tastier spaghetti with 2-step versus 3-step rods, you just get cruder matching of the air/fuel ratio to the engine's needs, with the resultant bad effects: more fuel consumption and resultant increased oil dilution and engine wear, etc.

Multistep power valves (of whatever configuration in any given brand/model of carburetor) did make for cleaner exhaust, as one of many favourable results of their phase-in.
Carter jets and (especially!) rods are something of a black art. Unlike Holley's simple, sequential numbering system – a 56 jet is bigger/richer than a 55 and smaller/leaner than a 57 – Carter's jet and rod numbers don't all or always follow a consistent, logical numbering system. It's a little like comparing the metric system (a 10mm wrench is smaller than an 11 and bigger than a 9) to the US Customary system (a 9/16" wrench is smaller than a 19/32 and bigger than a 31/64").
Yeah, I thought so. Hallucinated nonsense from the same "AI" that confidently (and incorrectly) asserted that the Slant-6 distributor drive gear has 18 teeth when I tried asking it. Do yourself a large favour and quit thinking it is at all a reliable source for answers to any kind of technical question, even just to see what it says, as a starting point.

This word-salad it spewed out for you (in confident, take-it-from-me tones, of course) is a result of it "reading" a bunch of ignorant noise in web forums and articles (of much lower quality than we tend to get on here), which all boils down to pretty much "HURRRR! DERP!!! EMISSION CONTROLS ARE POOPY!! HULK SMASH THEM SO CAR RUN BETTER!"
There are a lot more moving parts to this question than just the jet and rod. "1.25 inch BBD" covers a large range of significantly different carburetors. That "1.25 inch" just refers to the carb mount bolt pattern. There are numerous different venturi sizes, different airhorn sizes, different air bleeds, different throttle plate setups, might be different throttle bore sizes as with the BBS, etc.

Generally speaking, a 225 will run fine with a (real) 273 or 318 BBD in good condition, jetted as built, and no jetting adjustments are warranted for E10 versus E0 (gasoline with no ethanol in). E10 contains about 3% less energy per unit volume than plain gasoline – not enough to be worth rejetting for. Seasonal and altitudinal variations (air temperature and oxygen content) exert bigger effects.

All bets* are off with the Chinese copycats.

*Including the one where you gamble your car won't burn down

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

How would you explain that Mikes Carburator Parts has a bunch of 2-step BBD rods for sale, but no 3-step rods?

Why is that a question relevant to your original one, and why would I have an authoritative answer for it? Hey, how would you explain that Sears Craftsman lawnmowers came with Tecumseh engines for many years, and not Briggs & Strattons?

I can think of some solid, plausible reasons why Mikes Carburetor Parts might have 2-step rods and not 3-step rods (hint to one of them: there are some carburetor parts I would really like to be able to buy, but can't, even from vendors with a bigger, more diverse product range than Mike's).

And I can also think of some baseless-nonsense answers that could be made to sound plausible, especially if repeated and amplified in web forums until they became 'common knowledge' (or ChatGPT manure).

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Maybe it's because nobody wants them, which would corroborate what the AI said about them?

Maybe frogs have teeth and claws, and live in toilet bowls!

Seriously: maybe Mike's doesn't have 'em because nobody asks for 'em. Maybe because they're not available. Maybe because they're available but so expensive nobody would buy one. Maybe some other reason. Could it all align with what the "AI" said? Yes. I don't think it's likely.

I wonder if you really meant your first question ("Is this true?"). It seems more like you're primarily interested in getting support on here for what the "AI" told you.

Another thing: there are many, significant differences between the Chrysler-spec BBDs and the BBDs used in other applications. The ones used in AMC/Jeep vehicles, for example, are troublesome in ways the Chrysler ones aren't. Think about how that might colour and shape the output of an "AI".

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Back when I was considering a carbed turbo setup, I was seriously considering machining continuous-curved metering rods instead of stepped. In the end, I rejected that and went EFI because I didn't want to buy a micro lathe and learn how to use it just to tune a carb, but even a 3 step rod is a compromise. Engine fueling needs don't take drastic steps so much as continuously transition into each other with no real stopping points - even between on boost and off boost.

Now that's the theory. The difference between theory and practice? In theory, there isn't one...

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Matt Cramer
1966 Dodge Dart turbo / EFI project

That's one of those ideas that looks great in practice, but in theory it'll never work!

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

And FWIW, I have had two separate times where I've had to pull a frog out of the toilet bowl. Guess they just head for the largest body of water on my property.

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Matt Cramer
1966 Dodge Dart turbo / EFI project