Once you have the gas valve disassembled, take a small screwdriver and pick and scrape out the built up carbon, then take a torch tip cleaner (Pictured. You can get one at any hardware store for a few bucks) and file clean the gas ports. I feel that the gas system being difficult to clean as some say is highly overblown...it's really quite simple and a very well designed system that doesn't need to be cleaned very often.
Tron.