I have a 1978 kz750 and the motors seem real bullet proof. The bike has allot of vibration and on long rides gets old fast. I don´t think so much it to be a tire balance issue, as when I pull in the clutch doing seventy mph it´s real smooth. Once you release the clutch all the vibration kicks in on the large 2cyclinder motor. Doing 80 sure feels squirly... If your mechanicly inclined they are pretty easy to work on. The motor does not have to come out of the frame to get to the generator... Overall I like it. Trying to maybe turn it into a cafe racer is cool but bar end mirrors are no good as they do not stay true, always moving around no matter what you do from all the vibration.