Carburetor system for outdoor power equipment

1. An engine, comprising:

a fuel tank;

a well configured to hold fuel delivered from the fuel tank;

an air intake;

a combustion chamber;

a passageway configured to channel air from the air intake to the combustion chamber, wherein the passageway comprises a surface at least partially defining a constricted section of the passageway, and wherein the surface is configured to be adjusted to change the area of the passageway through the constricted section;

a nozzle in fluid communication with the well and directed into the passageway proximate to the constricted section, whereby the constricted section of the passageway provides a relative low pressure in air passing through the passageway that draws fuel from the nozzle to the air;

a vent configured to connect the well with outside air; and

a variable restrictor configured to limit the connection provided by the vent between the well and outside air, wherein the degree of restriction provided by the variable restrictor is a function of the area of the constricted section of the passageway.

2. The engine of claim 1 , wherein the variable restrictor is configured to increasingly restrict the vent as the area of the constricted section of the passageway increases.

3. The engine of claim 2 , wherein the variable restrictor is mechanically coupled to the surface at least partially defining the constricted section of the passageway.

4. The engine of claim 2 , further comprising a shaft, wherein the surface comprises a contour on the shaft, and wherein the surface is adjusted by moving the contour relative to the passageway.

5. The engine of claim 4 , wherein the variable restrictor comprises a second portion of the shaft, whereby rotation of the shaft simultaneously adjusts the area of the constricted section and the degree of restriction provided by the variable restrictor.

6. The engine of claim 1 , further comprising a manual control for adjusting the surface to change the area of the constricted section from outside of the engine.

7. The engine of claim 1 , further comprising a controller configured to operate the surface as a function of engine load.

8. The engine of claim 7 , wherein the controller comprises an actuator that is pressure-sensitive and configured to be responsive to changes in vacuum pressure of the engine.

9. The engine of claim 8 , wherein the actuator is coupled to the passageway further from the air intake than the constricted section is from the air intake.

10. Outdoor power equipment, comprising:

a frame;

wheels coupled to the frame;

a fuel tank;

an engine mounted to the frame, comprising:

an air intake;

a combustion chamber;

a passageway configured to channel air from the air intake to the combustion chamber, wherein the passageway comprises a surface at least partially defining a constricted section of the passageway, and wherein the surface is configured to be adjusted to change the area of the passageway through the constricted section;

a well configured to hold fuel delivered to the well from the fuel tank;

a nozzle in fluid communication with the well and directed into the passageway proximate to the constricted section of the passageway, whereby the constricted section of the passageway provides a relative low pressure in air passing through the passageway that draws fuel from the nozzle to the air;

a rotating tool driven by the engine;

a control interface configured to allow an operator to adjust the surface at least partially defining the constricted section of the passageway when the engine is in a wide-open throttle configuration, thereby changing the area of the passageway through the constricted section.

11. The outdoor power equipment of claim 10 , wherein the engine further comprises:

a shaft, wherein the surface at least partially defining the constricted section of the passageway comprises a contour on the shaft; and

a throttle plate located along the passageway and having a cam coupled thereto, wherein the cam interferes with the shaft, preventing rotation of the shaft when the throttle plate is oriented to partially close the passageway.

12. Outdoor power equipment, comprising:

a frame;

wheels coupled to the frame;

a fuel tank;

an engine mounted to the frame, comprising:

an air intake;

a combustion chamber;

a passageway configured to channel air from the air intake to the combustion chamber, wherein the passageway comprises a surface at least partially defining a constricted section of the passageway, and wherein the surface is configured to be adjusted to change the area of the passageway through the constricted section;

a well configured to hold fuel delivered to the well from the fuel tank;

a nozzle in fluid communication with the well and directed into the passageway proximate to the constricted section of the passageway, whereby the constricted section of the passageway provides a relative low pressure in air passing through the passageway that draws fuel from the nozzle to the air;

a rotating tool driven by the engine;

a control interface configured to allow an operator to adjust the surface at least partially defining the constricted section of the passageway when the engine is in a wide-open throttle configuration, thereby changing the area of the passageway through the constricted section; and

a locking system, wherein when the engine is not in the wide-open throttle configuration the control interface is locked by the locking system, preventing the operator from being able to adjust the surface.