Fuel control system

1. A charge forming device, comprising:

a body having a main bore;

a fuel metering assembly including a diaphragm that defines at least part of a fuel chamber from which fuel is provided to the main bore and a reference chamber separate from the fuel chamber;

a passage communicated with a subatmospheric pressure source and with the reference chamber, wherein the pressure source is the main bore; and

an electrically actuated valve having an open position and a closed position, and wherein the valve at least substantially prevents communication of the pressure source with the reference chamber when the valve is in the closed position and permits communication of the pressure source with the reference chamber when the valve is in the open position to vary the rate of fuel flow from the fuel chamber wherein the passage extends at least partially through the body and through a portion of the diaphragm.

2. The device of claim 1 which also includes a metering body coupled to the body and defining part of the reference chamber, wherein the metering body includes a vent communicating atmospheric air with the reference chamber.

3. The device of claim 2 wherein the minimum diameter of the passage is greater than the diameter of the vent.

4. The device of claim 2 wherein the minimum cross-sectional area of the passage is greater than the cross-sectional area of the vent.

5. The device of claim 2 wherein at least part of the passage is formed in the metering body, and wherein the valve is carried by the metering body, the valve includes a valve head and the metering body includes a valve seat engageable by the valve head when the valve is in the closed position.

6. The device of claim 4 wherein the minimum cross-sectional area of the passage is between 3 and 10 times greater than the cross-sectional area of the vent.

7. The device of claim 1 which also includes a throttle valve having a valve head received at least partially within the main bore and wherein the passage is communicated at one end with the main bore at a location downstream of the throttle valve.

8. The device of claim 1 which also includes a throttle valve having a valve head received at least partially within the main bore and wherein the passage is communicated at one end with an area downstream of the throttle valve.

9. The device of claim 5 wherein the diameter of the passage upstream and downstream of the valve seat is greater than the diameter of the vent.

10. A charge forming device, comprising:

a body having a main bore;

a throttle valve rotatably carried by the body and having at least a portion received in the main bore;

a diaphragm with a first side that defines at least part of a fuel chamber from which fuel is provided to the main bore and a second side that defines at least part of a reference chamber that is separate from the fuel chamber;

a passage communicated with a subatmospheric pressure source and with the reference chamber; and

an electrically actuated valve having a valve head that is moveable between an open position and a closed position relative to a valve seat, the valve seat is located between the pressure source and the reference chamber and the valve at least substantially prevents communication of the pressure source with the reference chamber when the valve head is in the closed position, and the valve permits communication of the pressure source with the reference chamber when the valve is in the open position to vary the rate of fuel flow from the fuel chamber wherein the pressure source is the main bore and wherein the passage extends at least partially through the body and through a portion of the diaphragm.

11. The device of claim 10 wherein the passage is communicated at one end with the main bore at a location downstream of the throttle valve.

12. The device of claim 10 which also includes a metering body coupled to the body and defining part of the reference chamber, wherein the metering body includes a vent communicating atmospheric air with the reference chamber.

13. The device of claim 12 wherein the minimum cross-sectional area of the passage is greater than the cross-sectional area of the vent.

14. The device of claim 12 wherein the diameter of the passage upstream and downstream of the valve seat is greater than the diameter of the vent.

15. An engine system, comprising:

an engine including a spark plug;

a charge forming device, including:

a body having a main bore communicated with the engine;

a fuel metering assembly including a diaphragm that defines at least part of a fuel chamber from which fuel is provided to the main bore and a reference chamber separate from the fuel chamber;

a passage communicated with a subatmospheric pressure source and with the reference chamber; and

an electrically actuated valve that is moveable between an open position and a closed position to at least substantially prevent communication of one or more subatmospheric pressure signals from the pressure source with the reference chamber when the valve is in the closed position and to permit communication of one or more subatmospheric pressure signals from the pressure source with the reference chamber when the valve is in the open position to vary the rate of fuel flow from the fuel chamber wherein the pressure source is the main bore and wherein the passage extends at least partially through a portion of the diaphragm; and

an ignition circuit including one or more coils in which electrical energy is induced during operation of the engine, the ignition circuit being coupled to the spark plug to provide electrical energy to the spark plug, and the ignition circuit being coupled to the electrically actuated valve to provide electrical power to the electrically actuated valve.

16. The system of claim 15 wherein the ignition circuit includes or is communicated with a controller that controls the timing of when electrical energy is provided to the spark plug, and wherein the controller also controls the actuation of the electrically actuated valve between and among the open position and closed position.