Light throttle skip

My KDX220 under a light throttle has a skip. As soon as the engine is under a load, it goes away. The plug looks OK so I do not want to lean it out anymore. I played around with the idle mixture screw and it made no difference. Any suggestion? Thanks!

I went for a ride yesterday and tried adjusting the idle mixture screw like you said and it did not improve. Next, I richened up the needle jet by one clip and tried it and it was worse. So, I put the needle clip one position further up then I had it and it made a world of differance. The only problem is now I am in the leanest position on the needle jet and it seems like I could go a bit leaner. Is it possiable that I have another problem because the bike is stock other then an airbox mod. It seems odd to me that a stock bike is running rich in the leanest position on the needle jet. Thanks!