1. Wipe with a rag and carb cleaner.
2. Carefully scrape with a razor blade, new blade for each valve.
3. Scrub with a small ScotchBrite pad and carb cleaner.
4. Liberally spray off with carb cleaner.
I clean the valve pockets with a small piece of wooden dowel wrapped with a small piece of rag soaked in carb cleaner. I keep changing the rags until the pockets are clean. (make sure the piston is below the port)