This is an easy job and does wonders for getting rid of the bog that many with an FCR-MX (Only, regular FCR's use the 'Taffy Mod') experience. It can be done with the carb on the bike.
I use a #78 O-Ring (7/16" O.D. X 1/4" I.D. X 3/32" thick) from the plumbing dept. of nearly any home improvement/hardware store. Cost is about $2.00 for a box of ten, share with your pals!
1) Remove the throttle wheel cover from your FCR.
2) Work the O-Ring over the timing adjustment screw.
3) Pull the O-Ring over the black AP cam thusly.
4) Re-install the throttle wheel cover. Just that simple!
Images courtesy of DouglasGraham, staff photographer