If you get a chance to buy one of these, do it! I bought mine as an abandoned scrap for $400, but it came right back to life after some elbow grease. The carbs are a little tricky to get synched, but after you do, you better hold on! Extremely wide aftermarket for these bikes as well, plus you can pretty much put on any newer Kawa parts (like forks or the swing arm)to try to boost performance, but aside from replacing the steel frame, you´re better off just buying a more modern bike.
Summary: This bike is built for fun, not speed. If you want speed, get a GPz.