You need to buy a tachometer for a single cylinder engine to set your RPM's correctly.
To set the high rpm governor speed, place one end of the governor spring in the middle to lower hole in the "L" shaped governor lever, and place the other end of the spring in either the top or second hole from the top in the short lever that's located under the carburetor or on the flywheel shroud. (Follow the Kohler Service manual for this step.) It's best to use a small engine tachometer to determine the exact rpm to prevent over-revving of the engine, which could cause the connecting rod to break. The high speed governor limit for a stock engine is set at 3,600 rpm
I am going to purchase one of these when I get my 128 finished and am ready to start the motor.
http://www.tinytach.com/tinytach/index.php