I've got a Borrani rimmed CB750 rear wheel that I need to re-spoke and re-hub. The tire is off it, but the ends of the spokes were really rusty so I couldn't unscrew the spoke nipples. I dunked the rim in a tub of phosphoric acid to remove the rust on the spoke ends, and to my surprise, it cleaned the rim up really well.
It will need to be polished again, but all the crud and corrosion has gone, so it'll be a piece of cake without all the crud to deal with. Of course, Borrani rims are good quality aluminum whereas our carbs are crap quality "pot metal", so they'd probably dissolve in the acid. I've got a few old sets of carbs sitting in my garage though, so I might try one, just for fun. Cheers, Terry.