Stock jetting on most KDX models is too rich, especially if you ride at higher elevations.
You can lean out the low rpm range by turning out the air screw. This is a small brass screw on the left side of the carb, near the rear of the carb, above the float bowl. Measure how far it is out by turning it in and counting the turns. If it was less than 2 turns out, set it at 2 turns. Turning it out will lean the low rpm range. After 3 turns out, it won't make any more difference and you would need to put in a smaller pilot jet.
On the needle, if you put the clip into a higher groove, that will also lean out the mid range. Changing the clip position is something you can do for free. It pushes the needle farther into the needle jet, letting less fuel past. FWIW, most KDX models benefit from a thicker needle, which leans out the mid rpm.
The '86 - '88 models are known to run pretty strong at high rpm. With some attention to your airscrew, pilot jet and needle, you should be able to improve your low and mid range power and throttle response, without hurting the top end power.