Actually, you may use more fuel, but you get MORE POWER from the fuel you use. You'll notice the the bike just rides better after you put the new pipes on and get it tuned correctly. You're just improving the breathing of the whole system. As far as what a jet "KIT" is, it's less than what it sounds like. For around $70, you'll get a smaller needle, a larger main jet, and some instructions you can get for free at dynojet.com. You can do this mod yourself if you know a little about carbs. You can just buy a smaller needle and the larger main jet. I just bought an 800 Classic, and all I did was remove the idle/air mixture screw plug under the carb (It comes plugged it so you can't change it). I backed it out a few more turns (gives it more fuel at and around idle). Then I removed the jet needle and shimmed it up about 1/16" to get more fuel in (this controls fuel flow in the mid-throttle range). You may also want to look into a higher flowing air filter, such as the K&N. I also found some instructions on how to remove the baffles from my stock exhaust. The bike sounds awesome now, and runs like a top! Let me know if you want any more info.