Bigger version of the Z200 which didn’t last so well. Poor running at high revs may just be a split carb diaphragm. Vibration’s something of a killer above 70mph and handling goes off on worn suspension and tyres. Chains last 6k, so check around the back of the crankcase for cracks in case one’s broken. Most were out of the game by 30k. KL250 engine bits can be used to keep an old one running.