I blasted (using either glass bead or aluminum oxide - I can't remember which) an old Zenith updraft carb for my dad's Fjord AA. There was so much gunk and surface rust on it that it went through a treatment of blast, soak in carb cleaner, dry, repeat for a few weeks before it was completely clean. After three or four rounds of that, and a fresh powder coating job and a rebuit kit, it runs great.
