I like B-12 but it is wicked, Especially if it splashes into the eyes... Ask me how I know lol. Don't use it to clean parts before welding on them either.
Imo if you used it as a fuel additive to clean out the carbs it likely won't work.
There aren't many pieces to the carbs so with a Clymer and a little mechanical aptitude you'll be fine digging into them yourself.