The Holley 1920 on my slant six is not original. It does not have an id tag. How can I id the carb so I can get the correct replacement float and rebuild kit? The critical thing is the needle valve. Mine needs replacement and several different rebuild kits have had the wrong valve.

I also have a box of "mystery" carbs that I would also like to ID.

Lastly, what is a good home brew for dipping dirty carbs?

The 1920s don't use an ID tag. The ID number is stamped into the skyward- or forward-facing portion of the carburetor casting (not the float bowl) adjacent to the fuel inlet needle and seat. It's a 4-digit number usually followed by (irrelevant) letters. There were two different floats used in the 1920. Both were made out of nitrophyll. One weighed 7.5g, the other 12.5g. Only one of them is still available, and I don't recall which.

Which "needle valve" are you trying to replace? They are all interchangeable on the various 1920s, though there have been various differently-made styles. The idle mixture needle screw is not included in a rebuild kit.

Depending on how gunky the carb is, denatured alcohol, lacquer thinner, and acetone can be combined to make an effective carb dip.

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