Simple Green or Dawn dish liquid does wonders. I use Dawn for cleaning watch cases, which can either be solid gold/silver or plated over brass.
For carbs, I personally am a little hesitant to use a water-based cleaner, so I first hose down with carb cleaner, then I use an ultrasonic solution called Hi-Tech cleaner and Hi-Solv rinse made by Zenith. It dissolves grease and oil with ease, and the rinse cleans out the cleaning solution and either use the sun or an oven heated to 200 degrees for 1 hour to dry.