Abstract: A portable tool including a frame, a working element on the frame and a power unit for operating the working element. A switch on the frame switches between a first state, e.g., stop operation, and a second state, e.g., running operation. An actuator on the frame is repositionable relative to the frame to selectively change the switch from its first state into its second state and in a first path to change the switch from its first state into its second state. The actuator is mounted for movement relative to the frame in a second path that is different than the first path to change the switch from its first state into its second state.

Abstract: A portable power unit for operating a tool is provided and includes a frame adapted to be carried on the back of an operator to orient the power unit in a the predetermined operating position with the operator standing upright. The power unit further includes an engine mounted on the frame for powering a tool, a fan mounted between the frame and the engine, a fan intake positioned between the frame and the fan, and structure for attenuating engine and fan generated noise and for inhibiting the emanation of engine and fan generated noise in horizontal directions from the power unit with the power unit in the operating position.

Abstract: An internal combustion engine has a carburetor for mixing fuel with air entering through an inlet. A heat exchanger is mounted onto the carburetor air inlet so that heat from the heat exchanger is conducted to the carburetor housing. The heat exchanger has a plurality of channels through which air from an air cleaner pass on the way to the carburetor. An electric heating device attached to said heat exchanger and a first thermostat controls the electric heating device to raise the temperature of the heat exchanger when the fuel-air mixture falls below a given temperature. A second thermostat senses the temperature of the heat exchanger and prevents the temperature from exceeding a level at which a user's skin will blister if the exchanger is touched accidentally. In cold operating environments, the heat exchanger assembly raises the temperature of the air above the dew point, thus effectively lowering the relative humidity.