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Governing
While some people think that a governor on an engine is to prevent over speeding, the real purpose
in the small engine field is to maintain a desired speed regardless of load. With a fixed throttle position, the engine could speed up if the load was lightened, if the load is increased the engine would slow down or even stop.
A governor on the other hand will close the throttle if the load is lightened or open the throttle to
obtain more power if the load is increased. Basically, governors consist of two types - the pneumatic or air vane type and mechanical or flyball weight type.
The pneumatic governor is operated by the force of the air from the flywheel fins. When the engine is running, the air from the fins pushes against the air vane. The air vane is connected to the carburetor throttle by means of a link. The force and movement of these parts tends
to close the carburetor and thus slow down the engine speed.
Opposed to this is the governor spring which tends to pull the opposite way, opening the throttle. This spring is usually connected to an adjustable control of some kind so that the tension on the spring will
increase the engine speed. Decreasing the tension will lower the engine speed. The point at which the pull of the spring equals the force of the air vane is called the “governed speed”.
The mechanical governor, works in a similar manner except that instead of the force of the air blowing against the vane, we have the centrifugal force of flyball weights opposing the governor spring.
In either case, operation is the same. As the load on the engine increases, the engine will start to slow
down. As soon as this happens, the centrifugal force of the flyball weights lessens. This allows the governor spring to pull the throttle open wider increasing the horsepower to compensate for the increased load and thus maintain the desired governed speed.
If the load on the engine lessens, the engine starts to speed up. This will increase the pressure of the centrifugal force and the spring will be stretched a little farther thus closing the throttle and reducing the engine power. A properly functioning governor will maintain this desired speed within fairly close limits. He will obtain the long service life that is built into the engine at the factory.
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