It should be self-adjusting, If it is indeed the problem then you will have to either replace it with another self-adjusting tensioner (witch would be easier, and less likley to do the wrong way) or a manual tensioner ( witch is popular, but proper adjustment is critical leaving room to possibley do as much harm as good).
I'm not tring to push you in any one direction here, Just want you to be able to make as informed of a choice as possible. I believe that uncle jeff has responder to several post concerning the manual tensioner as well as others. So, do a couple more searches and read up. it may offer some more insight to witch way to go. good luck!!
CBR929-jardine race can, down 1, polished frame and swing arm,wheels polished, HELI bars, Sargent seat, Puig racing screen