Hi dougjc,
From the year of your bike I'm guessing it’s pretty much new. Chances are good one of the following is your problem; 1) the float level was set too high from the factory and needs to be adjusted, 2) there is some debris stuck between the float needle and its seat preventing it from closing properly or 3) the frame work around the float is tweaked a little causing the float to hang up/stick a little.
While you have the float bowl off to address the float level it would be a good time to make some jetting adjustments as well, assuming your still running stock jetting.
New KDX? - be sure to service your suspension linkage soon if you haven't already.
David