So, right before I put my bike away for the winter I did the whole jet kit and K+N job to try and get a few more Hp from my '90... Now if I am really aggressive with the throttle it gets up and goes really well but if I roll on the throttle slowly it hesitates for a second before it revs up.... it feels like it is bogging just a bit as I open up the throttle... my guess is that the fuel mix is a little ritch....

Does anybody know if an ignition advancer will help this at all?? Maybe just a good carb sync?

 

Mine used to do this all the time. Running race gas took care of it and letting the motor warm up for about 30 seconds would help as well. I got it all worked out when the carbs were rejetted and adjusted.
Also your plug wires could be corroded and that would cause a hesitation. I mean seriously, the wires are probably 17 years old! Mine were..
Good luck