The RB carb mod is actually very popular for the 220's i'm sure a search would show some good info, i have a 99 kdx220 with fmf rev pipe airbox mod, boysen power reeds, weisco piston and the RB carb mod, i bought the bike with the mod so i really can't tell you what it was like before the mod but the guy i bought it from said it gave him more power everywhere and made the bottom end 4 stroke like, said he could chug the bike nicely. i found that the jetting was a little picky but once you got it dialed in hold on, course i also have the rev pipe as opposed to the torque pipe, the torque pipe is great for the 200's but doesn't do much for the 220's, it will give them a gain down low but no noticable gain up top, the rev pipe will give a little bit on bottom and a lot more on top, and i don't have any problems starting it, first or second kick but it's all in the jetting, so in my opinion the RB mod is definetly worth it