John, between KXCam and myself, we have done days of research on surging. Here is my conclusion, the only way to clear it is to run way rich on the pilot and needle. If somebody with a KX5 has no surging (bucking) they are running rich, which you would NEVER know without trying to run leaner. I have tried EVERYTHING!! Including the fact that I'm running VP C12 (108MON) at 50:1 on MC1. I have done extensive work on the engine, including a big bore and porting, suring is very rampid and does not bother me. It runs great and is nothing wrong with the bike. I have now turned off my idle so I don't have to worry about the bucking while slowing down in a turn. I have tried diffrent fuels, every jet, a new carb, new #6 slide, timing, and much much more.. Want 50% of the details? Read the long jetting thread.
Cam is the man in this area, it was all his suggestions and my labor that got the conclusion, it is just the way the cookie crumbles and I'm just fine with it. If your KX does not surge, please give details on what you have and symptoms I guess.