So often we seem to have members & newbies post questions about an engine that is hunting or running poorly, either with or without a load on it. Our stock answers seems to be "clean the carb" or "check the fuel system". But here is another, admittedly rarer, cause. This is a Tecumseh OHV125 203032B (H) A.K.A Tecumseh Formula 12.5 hp.
The governor arm bushing (red arrow) is shot. The bushing connects the governor arm to the throttle rod, which turns the throttle shaft (green arrow) on the carb to increase or decrease engine speed (clear as mud??). I've used a rubber band (blue arrow) to take up the slack in the bushing so that the throttle rod does not rattle around in the bushing & make the engine hunt.
In video one, the rubber band has been removed. Watch the carb's throttle shaft & the governor arm.
In the second video, I've re-installed the rubber band. Notice the dramatic improvement.
The bushing (Tecumseh 36288) is $2.13 and the governor arm with bushing (Tecumseh 36284A) is only $2.08. Don't ask me why.