My father's lawnboy - rev's high and doesn't come down...

[netrate]

My father has this lawnboy :

Tru-Start Lawnboy 6.5 ft-lbs gross torque. Powered by Kohler 149cc with Smart Choke
20 inc mulching/rear bagging mower
Model number 10605 / 10625- serial number 311000001

Its an older model, maybe 10 years plus. He took it to a lawn mower repair person years ago and they said they didn't know why it is revving so high, so I thought I would ask here before my father sends it to the scrap heap. It is almost like switching gears in a manual transmission , but it continues to red-line.
Any suggestions to try?

 

[bertsmobile1]

Over reving 4 stroke mower engines is usually because the governor has failed
The test is to start the engine then grab the governor arm and move it by hand
If the engine responds to the position of the governor arm , which is what actually moves the throttle butterfly , but races away when you let it go then the governor is not doing its job
Pull the air cleaner housing off & take some photos so we can look at how it is connected

 

[Rivets]

This manual might be of some help. http://www.kohlerengines.com/engines/onlinecatalog/pdf/sm_14_690_01.pdf