Well for your YZF 600 you can get a factory pro ignition advance (about $70). Get "stage 3" jet kit ($100), drop in K&N filter ($70), and a FULL Arrow or Vance and Hine exhaust, etc. ($400-700). From my experience you should have around 90-95whp with those mods. You would need some experience if you wanted to install the jet kit yourself. Those Kehin carbs are bastards on that engine, I have a 98' YZF engine and it will be getting my sweet FZR Mikuni carbs installed on it.