Kohler is a manufacturer of a variety of small engines commonly used on lawn tractors and for commercial applications. Kohler engines are equipped with a governor that is designed to increase the throttle when the engine is under a heavy workload, then lower the throttle when the workload lightens to prevent damage to the engine from over-revving. Adjust the engine governor if your Kohler 25-horsepower engine is running roughly.
Disconnect the spark plug wire from the tip of the spark plug, and secure the wire well away from the spark plug.
Loosen the screws that secure the air filter to the carburettor, and remove the air filter.
Check the linkage spring that connects the governor arm to the throttle control on the top of the carburettor. If the spring is stretched or broken, replace it with a genuine Kohler governor linkage spring.
Loosen, but do not remove, the nut on the bottom of the governor arm where it connects with the governor shaft with an open-end wrench.
Grab the governor shaft with a pair of needlenose pliers, and rotate it counter-clockwise as far as it will turn. Hold it in place, and pull back on the governor arm before tightening the nut at the base of the governor arm with an open-end wrench.
Reconnect the air filter to the carburettor, and attach the spark plug wire onto the tip of the spark plug.
Start the engine, and allow it to warm up for about five minutes before putting the engine under various workloads to see if the engine runs smoothly under any load.