You had better check the setting of the throttle control cable and handle on the dash-board. It might have gotten disconnected, at the carburetor. and the throttle handle moves, but doesn't change the position of the cable. Or the throttle control on the carburetor. Sound like you need professional help. It is far cheaper than an engine that goes:"BANG"! At that point, your main revving problem will be solved. Also solved will be the fact that you needed professional help, but didn't want to pay the price!

What engine make and model? The high rev- can you manually slow it down by holding the throttle shaft? If you are unsure take it in- Rusty has a good point.

Model is Kawasaki FV500V i believe and was looking at possible governor control spring as far as mechanical link problem will check cable connection as well.