3 Types: Pneumatic: Common to smaller, vertical engines (push mowers). A plastic air vane next to the flywheel fan that is attached to the throttle. A spring is also attached to the throttle or vane. Spring tries to open throttle, vane tries to close it. Air from the fan pushes on the air vane. Faster the engine spins, the more air is pushed against the vane, closing the throttle. Mechanical: Any larger vertical engine, most horizontal engines (tillers, riding mowers, etc.). A gear inside the engine has weights attached, as the engine speeds up, these weights spread outward, pushing on a rod that sticks out of the engine block. This rod has a linkage directly to the throttle, closing it as the engine speeds up. A spring (usually a couple) tries to counteract this motion, the balance between them determines engine speed. You will see a rod come out of the block that rotates. Attached to this w/ a pinch bolt is the gov. arm, which is usually 3-5" long, with multiple holes for adjustments. This will have a rod linkage near the end of it, which attaches to the throttle. Electronic: Larger, premium applications (generators). Speed-sensing device on engines sends signal to electric actuator motor on throttle. Necessary when precise throttle and speed control are required.
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