Plynn41   has good advise.  On  any mx bike you should have to push on the bars  to move the bars when the bikes on a stand.  The bars should stop and not move, when  you stop pushing on the bars  with your palm  on a  stand.  On  04-07  cr125,s  you can  run up to  110 mm  of sag,  most  bikes  you can  run  more sag than the book says.   I rode a pals  01 cr125,  no head shake at all.  Alot of  riders  put there body weight on the bars  and not on the pegs.  Once you relax  and  keep your body weight on the pegs,  you,ll rip.