Abstract: A dynamometer system for applying a controlled variable operating load against the blade of a rotary-type lawn mower while the mower is in stationary operation atop the system. The system includes a frame for supporting and securing the lawn mower thereupon, a dynamometer having an input shaft connected to the frame, the input shaft of the dynanometer including at its distal end a rotary-type blade engaging crossbar. By this arrangement, a controlled load may be applied by the dynanometer against the rotating blade and thus the motor of the lawm mower while it is operating in stationary position atop the frame to aid in testing, diagnosing problems, and adjusting the motor. The dynamometer is preferably hydraulic, although it may also be of the electric absorption or mechanical absorption type.