See if you can stabilize the engine RPM by finding the solid link between the governor arm and the carburetor throttle and holding it steady with a pair of pliers while the engine is running. Wear safety glasses and be extremely careful not to touch any moving parts when doing any troubleshooting with a running engine. If this stabilizes the RPMs, the governor sensitivity adjustment should be checked. Consult your service manual for more information.
If this does not fix the revving issue with your Tecumseh small engine, check for any problems with bent or worn linkages or a weak governor spring.
You can find the model and serial numbers either on the starter housing or on a plate or tag bolted to the crankcase area.