RB Designs is a good one, my carb was done by them, i have a 99 KDX220, course i bought it with done so i don't know what it's like without it, the guy i bought it from said it helped, better throttle response, and better power, my bike had a torque pipe on it when i got it which is pretty pointless for 220 cuz it will only gain down low and no top, so i'll be getting a rev pipe shortly to hopefully open it up some more, here's there website
www.rb-designs.com