Oh yeah, straight pipes have to have the carbs jetted for that. You can burn the exhaust valves. Either bring it to a dealer, or get the Factory Manual. You can find them online for free in .pdf form. Not allowed to post links. Get a Kawasaki Factory Service Manual, not some Hayes, or Chilton. If you don't know how to adjust valves, best if you bring it to someone, or really commit to it. Get a proper muffler for that bike. I'm sure there are a ton of them on EBAY, and they made so many of those bikes, they can had cheaply. You'll get more power too, as you lose a lot of mid-range with straight pipes, especially if the carbs are set up for it, carbs of fuel injected, it has to be set up for that.