When refreshing your carb don't forget to replace the floating valve seal. Carb cleaners and time will degrade this seal and negatively affect idle stability and throttle response.
Here's a How-To that will show you how to replace this seal:
http://crfsonly.com/howto/keihin-fcr-ca ... rf450r.php
Please post comments or questions about this How-To or seal in this thread.
Ken