We have a demo unit- 52 " super Z w/ 25HP kaw w/ BacVac. Demo going along great all day. Suddenly engine started over speeding as if stick got into governor spring. Not the case. Engine clean. We would reduce the RPMs manually and control engine speed OK but then RPMs would drop way down (as if engine was normal in half throttle position). Upon increaing throttle control to normal max position, engine would eventually overspeed again. Any thoughts on this? Is this inherent to Kawasaki 25HP? Is this just a fluke? Should we avoid buying this machine???? We love its performance otherwise!