Toro S-620 Snowthrower governor

The S-620 is one of those old single stagers with the straight blades and the little rubber vanes for directional control and a 2-stroke-cycle engine.
What kind of governor do these things have? Is it a little flyweight thing inside the engine or air vane or something else? The reason I ask is because I have one that starts and runs ok but wade into any snow and the speed drops to the point of stalling and seems to be running on a fixed throttle. I took the cover off and tried to watch for any movement of the throttle and there is none so that's kind of confirmed but not the reason why. It's got the spring tugging the throttle in the open direction and the little wire link coming from points unknown. If it's an internal engine part then it's not really worth fixing on such an old machine.
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