get a new plug, warm up the bike on an old plug, switch the spark plugs and go WOT through all the gears then kill the engine and glide to a stop. then put the old plug back in and go home. then cut the threads off the new plug you ran WOT with and see what color the ring at the base of the white part is. it'll determine if your running rich, lean or perfect.
if you dont get what im sayin do some searching, its a pretty common topic.