Hi, Ensure that you do not run the engine until the problem is resolved. Over revving will cause catastrophic engine failure. That said, the governor assembly is vary sensitive and should only be serviced by a certified small engine mechanic or some that has extensive experience with small engines. There are several possibilities that could cause your issue; the governor spring has broken or fallen off, the linkage is dirty and sticking, the throttle plate/shaft is worn and stuck open, the internal governor gear has failed. Inspect the linkage to ensure it moves freely and the throttle shaft on the carburetor moves freely. Ensure the spring is in place the controls the throttle rod the goes from the throttle control linkage on the engine and the throttle on the carburetor. move the throttle control to full speed then manually close the throttle on the carburetor, you should feel a slight resistance when moving the throttle plate on the carburetor back to idle. Next move the throttle control to full slow and repeat, the throttle should be in the idle position on the carburetor. Lubricate all linkages with light weight oil. If all seems in order and you have lubricated the linkages, re-start the engine being prepared to immediately shut it off if it over revs. If it does not operate properly after your inspection, corrections and lubrication, I recommend having a Sears technician service the tractor. You do not want to destroy your engine, better safe than sorry.
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