seems like you are bottoming the fork, not normal unless you weigh 15 stone, have sagged out springs, or lost most of your fork oil. first suggestion would be to drain oil from forks the proper way, that is, upside down over a pan. wash them out well, then refill with fresh 10wt fork oil to proper level as described in service manual. check length of springs against factory specs and replace if too short. if you have the much-desired centrestand, you're good.
Could also be loose head bearings, that would give a similar clunk, though you might feel that slightly through the bars