If you turn the fuel screw in until you get some popping when decellerating in gear, you have leaned out the idle circuit. If you can run the fuel screw nearly closed and the bike still idles without decel popping, then the idle circuit is running too rich for some reason.
Here is a nice summary on Keihin carbs. It's written for a different model but is very similar to the FCR.
I like this graphic. I helps isolate the parts of the carb to different throttle positions.