Variable venturi and zero droop vacuum assist

Outdoor power equipment, comprising:

• a frame;
• wheels coupled to the frame;
• a fuel tank;
• an engine mounted to the frame, comprising:
• a carburetor, comprising:
• a variable venturi having a fixed surface and an adjustable surface that form a constricted section, wherein the adjustable surface is movable between a narrow position in which the constricted section has a first area and a wide position in which the constricted section has a second area larger than the first area;
• a venturi lever coupled to the adjustable surface and configured to move the adjustable surface between the narrow position and the wide position;
• a throttle valve downstream of the variable venturi and configured to be movable between a fully open position and a fully closed position to control a fluid flow through the carburetor;
• a throttle lever coupled to the throttle valve and configured to move the throttle valve;
• and
• an intake port in fluid communication with the fluid flow;
• a governor assembly including a governor configured to detect an engine speed of the engine, a governor arm coupled to the governor, the venturi lever, and the throttle lever, and a governor spring coupled to the governor arm to bias the throttle valve towards the fully open position;
• and
• a vacuum actuator including an actuator housing, a pressure-sensitive member positioned in the actuator housing and dividing the actuator housing into a vacuum side and an atmospheric side, an input port in fluid communication with the vacuum side of the actuator housing and in fluid communication with the intake port so an engine vacuum at the intake port is communicated to the vacuum side, an actuator linkage coupled to the governor spring and also coupled to the pressure-sensitive member for movement with the pressure-sensitive member in response to the engine vacuum, and an actuator spring biasing the actuator linkage to increase the tension on the governor spring;
• and
• a rotating tool driven by the engine.

A method of operating an engine, comprising:

• governing an engine speed to a governed speed;
• applying a load to the engine;
• counteracting governor droop to maintain the engine speed at the governed speed;
• increasing the load on the engine;
• increasing a flow of fuel-air mixture through a carburetor in response to the increased load, wherein increasing the flow of fuel-air mixture is achieved by increasing the size of a restricted section of a venturi of the carburetor in response to an engine speed sensed by the governor;
• and
• indicating to a user with an indicator the increased flow of fuel-air mixture.