Whats the state of your tires and front suspension? If the tires aren't pretty new i'd start looking at them. if the are i'd probably consider when the fork oil was last changed and whether new springs might be in order. Are the springs stock? What about the spacers? Anyways, assuming the head is good those are the 2 things i would consider. Oh, and make sure the rear wheel alignment is on, plus as Phil said, pressures.
