A tamper resistant hourmeter is provided for an engine powered lawn mower. The hourmeter has a first pin connected to a positive voltage from a battery through a key actuated switch, a second pin to ground, a third pin to a magneto ignition, and a fourth pin to a fuel shutoff solenoid. The tamper resistant hourmeter connects the positive voltage from the battery to the fuel shutoff solenoid. The fuel shutoff solenoid opens a fuel line to the engine only if the key actuated switch is in either of the run or start positions.