buttafingaz has it nailed, but perhaps it didn't register due to his punctuation?
There's a spray cleaner called "Westley's Bleche Wite" that's available at most auto stores like Kragen, Trak, etc. I have used it for 30+ years on all my antique cars and bikes. There is nothing that can compare! Spray on, wait a couple of minutes, scrub with small brush or Brillo, rinse off. Don't get on painted surfaces.
It is caustic. Keep it out of your eyes, open cuts, and don't breathe the mist.
Bleche-Wite is the BEST!!!