Variable venturi and zero droop vacuum assist

1. An engine, 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.

2. The engine of claim 1 , further comprising:

a venturi link coupling the venturi lever to the governor arm;

wherein the governor arm includes a slot that receives a distal end of the venturi link.

3. The engine of claim 1 , wherein the intake port is downstream of the variable venturi.

4. The engine of claim 1 , further comprising:

a switch configured to be actuated when the governor arm is a position that moves the adjustable surface to the wide position; and

an indicator electrically coupled to the switch to indicate when the adjustable surface is in the wide position.

5. The engine of claim 1 , wherein at a first load on the engine, the governor arm is in a first position where the adjustable surface is in the narrow position, the throttle valve is not in the fully open position, and a first engine vacuum is communicated to the vacuum side of the vacuum actuator; and

wherein at a second load on the engine, greater than the first load on the engine, the governor arm is in a second position where the adjustable surface is in the wide position, the throttle valve is in the fully open position and a second engine vacuum, less than the first engine vacuum is communicated to the vacuum side of the vacuum actuator.

6. The engine of claim 5 , further comprising:

a venturi link coupling the venturi lever to the governor arm;

wherein the governor arm includes a slot that receives a distal end of the venturi link.

7. The engine of claim 5 , wherein the intake port is downstream of the variable venturi.

8. The engine of claim 5 , further comprising:

a switch configured to be actuated when the governor arm is a position that moves the adjustable surface to the wide position; and

an indicator electrically coupled to the switch to indicate when the adjustable surface is in the wide position.

9. The engine of claim 8 , further comprising:

a venturi link coupling the venturi lever to the governor arm;

wherein the governor arm includes a slot that receives a distal end of the venturi link.

10. The engine of claim 9 , wherein the intake port is downstream of the variable venturi.

11. 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.

12. The outdoor power equipment of claim 11 , further comprising:

a venturi link coupling the venturi lever to the governor arm;

wherein the governor arm includes a slot that receives a distal end of the venturi link.

13. The outdoor power equipment of claim 11 , wherein the intake port is downstream of the variable venturi.

14. The outdoor power equipment of claim 11 , further comprising:

a switch configured to be actuated when the governor arm is a position that moves the adjustable surface to the wide position; and

an indicator electrically coupled to the switch to indicate when the adjustable surface is in the wide position.

15. The outdoor power equipment of claim 11 , wherein at a first load on the engine, the governor arm is in a first position where the adjustable surface is in the narrow position, the throttle valve is not in the fully open position, and a first engine vacuum is communicated to the vacuum side of the vacuum actuator; and

wherein at a second load on the engine, greater than the first load on the engine, the governor arm is in a second position where the adjustable surface is in the wide position, the throttle valve is in the fully open position and a second engine vacuum, less than the first engine vacuum is communicated to the vacuum side of the vacuum actuator.

16. 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.

17. The method of claim 16 , wherein counteracting governor droop occurs in response to a change in an engine vacuum.

18. The method of claim 16 , wherein increasing the size of a restricted section of a venturi of the carburetor is achieved by moving an adjustable surface of the venturi relative to a fixed surface of the venturi.