Light surface rust can be taken off with steel wool, wire brush, or wire wheel. If you have a blast cabinet, glass beads or aluminum oxide will work. Phosphoric acid works good, too, as does Navel Jelly. If you are refinishing a painted air cleaner, strip all paint and rust off, prime with a good epoxy primer, and paint. If it's a chrome air cleaner, you can try glass beads or fine steel wool. If those don't do the trick, you'll have to send it out to get rechromed.
