Abstract: In at least some implementations, a locking plate may be received between the cover plate and the adjustable valve and be movable to a first position permitting access to the adjustable valve and a second position inhibiting or preventing access to the adjustable valve. In some implementations, a latch assembly may releasably retain the locking plate in its second position. The latch assembly may include a finger carried by the locking plate and releasably engageable with a stop when the locking plate is in its second position.

Abstract: In at least some implementations, a locking plate may be received between the cover plate and the adjustable valve and be movable to a first position permitting access to the adjustable valve and a second position inhibiting or preventing access to the adjustable valve. In some implementations, a latch assembly may releasably retain the locking plate in its second position. The latch assembly may include a finger carried by the locking plate and releasably engageable with a stop when the locking plate is in its second position.

Abstract: A carburetor with a body with a cavity in which an adjustable fuel valve is received. To inhibit access to and manual adjustment of the valve, a cover may overlay at least a portion of the adjustable valve. In some forms, a releasable lock plate may be received between the cover and the adjustable valve. Specialty tools may release the lock plate and adjust the valve.

Abstract: In at least some implementations, a method of maintaining an engine speed below a first threshold, includes: (a) determining an engine speed; (b) comparing the engine speed to a second threshold that is less than the first threshold; (c) allowing an engine ignition event to occur during a subsequent engine cycle if the engine speed is less than the second threshold; and (d) skipping at least one subsequent engine ignition event if the engine speed is greater than the second threshold. In at least some implementations, the second threshold is less than the first threshold by a maximum acceleration of the engine after one ignition event so that an ignition event when the engine speed is less than the second threshold does not cause the engine speed to increase above the first threshold.

Abstract: A power tool may include an engine, a tool driven for movement by the engine, a brake mechanism coupled to the tool, a charge forming device coupled to the engine and a transmission member operably coupled to the brake mechanism and a throttle valve of the charge forming device. The brake mechanism inhibits movement of the tool in an engaged position of the brake mechanism and permits movement of the tool in a disengaged position of the brake mechanism. The charge forming device is coupled to the engine to provide a combustible fuel and air mixture to the engine, and the throttle valve is movable between a first position and a second position. The transmission member is operably coupled to the brake mechanism and the throttle valve so that the throttle valve is moved away from the first position when the brake mechanism is moved to the engaged position.

Abstract: In at least some implementations, a method of maintaining an engine speed below a first threshold, includes: (a) determining an engine speed; (b) comparing the engine speed to a second threshold that is less than the first threshold; (c) allowing an engine ignition event to occur during a subsequent engine cycle if the engine speed is less than the second threshold; and (d) skipping at least one subsequent engine ignition event if the engine speed is greater than the second threshold. In at least some implementations, the second threshold is less than the first threshold by a maximum acceleration of the engine after one ignition event so that an ignition event when the engine speed is less than the second threshold does not cause the engine speed to increase above the first threshold.

Abstract: An apparatus for delivering a fuel-air mixture to an engine is provided. The apparatus includes: a carburetor having one or more passages and one or more chambers, wherein at least some of the passages and chambers are in communication with one another; and a fluid pump communicated with the carburetor and pumping fluid into or out of the carburetor to influence an fuel-to-air ratio of a fuel and air mixture delivered from the carburetor.

Abstract: A carburetor with a body with a cavity in which an adjustable fuel valve is received. To inhibit access to and manual adjustment of the valve, a cover may overlay at least a portion of the adjustable valve. In some forms, a releasable lock plate may be received between the cover and the adjustable valve. Specialty tools may release the lock plate and adjust the valve.

Abstract: A carburetor provides a supplemental fuel supply to an engine and includes a body, a fuel metering diaphragm and a fluid pump. The fuel metering diaphragm defines part of a fuel metering chamber and a reference chamber and has at least a portion that is movable relative to the body to increase and decrease the volume of the fuel metering chamber to control fuel flow in the fuel metering chamber. The fluid pump is carried by the carburetor or another component upstream of the carburetor and has an outlet in fluid communication with the metering reference chamber and an actuator arranged to discharge fluid through the outlet to increase the pressure within the metering reference chamber and thereby increase the fuel flow rate from the fuel metering chamber to the air-fuel passage to provide a supplemental fuel supply to the engine.

Abstract: An apparatus for delivering a fuel-air mixture to an engine is provided. The apparatus includes: a carburetor having one or more passages and one or more chambers, wherein at least some of the passages and chambers are in communication with one another, and a fluid pump communicated with the carburetor and pumping fluid into or out of the carburetor to influence an fuel-to-air ratio of a fuel and air mixture delivered from the carburetor.

Abstract: A carburetor provides a supplemental fuel supply to an engine and includes a body, a fuel metering diaphragm and a fluid pump. The fuel metering diaphragm defines part of a fuel metering chamber and a reference chamber and has at least a portion that is movable relative to the body to increase and decrease the volume of the fuel metering chamber to control fuel flow in the fuel metering chamber. The fluid pump is carried by the carburetor or another component upstream of the carburetor and has an outlet in fluid communication with the metering reference chamber and an actuator arranged to discharge fluid through the outlet to increase the pressure within the metering reference chamber and thereby increase the fuel flow rate from the fuel metering chamber to the air-fuel passage to provide a supplemental fuel supply to the engine.

Abstract: In at least some implementations, a carburetor having a fuel metering system including a diaphragm assembly that moves in response to pressure changes in a metering chamber to actuate a metering valve may include a flexible diaphragm adapted to carried by a body of the carburetor at a periphery to define part of the metering chamber. The portion of the diaphragm that defines part of the metering chamber defines a chamber projected area of the diaphragm. A backing plate is attached to the flexible diaphragm and arranged to be located outside the metering chamber. The backing plate having an outer perimeter defining a plate projected area, wherein an area ratio of the plate projected area to the chamber projected area is greater than about 0.1.

Abstract: A fuel and air supply device for an engine includes a carburetor having a fuel metering assembly with a fuel metering diaphragm defining at least part of a reference chamber, a scavenging air assembly including an air passage and an air valve moveable within the passage to alter air flow through the air passage, and a reference passage. The reference passage communicates at one end with the air passage upstream of the air valve and at its other end with the reference chamber to provide a reference air signal through the reference passage to the reference chamber. The reference air signal, in at least some implementations, is taken from a location downstream of an air filter and any other components so it is representative of the air flow at the air valve and accounts for restrictions to air flow caused upstream of the air valve.

Abstract: Supply of supplementary fuel is controlled through a supplementary fuel supply passage in a carburetor to an engine according to a variety of methods and devices.

Abstract: In at least some implementations, a carburetor having a fuel metering system including a diaphragm assembly that moves in response to pressure changes in a metering chamber to actuate a metering valve may include a flexible diaphragm adapted to carried by a body of the carburetor at a periphery to define part of the metering chamber. The portion of the diaphragm that defines part of the metering chamber defines a chamber projected area of the diaphragm. A backing plate is attached to the flexible diaphragm and arranged to be located outside the metering chamber. The backing plate having an outer perimeter defining a plate projected area, wherein an area ratio of the plate projected area to the chamber projected area is greater than about 0.1.

Abstract: A carburetor includes a fuel and air mixing passage with a throttle valve therein, and a bore with a valve therein defining in part a valve actuation chamber and a separate fuel and air mixing chamber in communication with the fuel and air mixing passage at a location downstream of the throttle valve. A fuel passage and an air passage are in communication with the fuel and air mixing chamber. A purge apparatus is in communication with the valve actuation chamber and is operable to move the valve to an open position to open the fuel and air passages to the fuel and air mixing chamber such that a fuel and air mixture may flow from the fuel and air mixing chamber to the fuel and air mixing passage downstream of the throttle valve.

Abstract: A carburetor includes a fuel and air mixing passage with a throttle valve therein, and a bore with a valve therein defining in part a valve actuation chamber and a separate fuel and air mixing chamber in communication with the fuel and air mixing passage at a location downstream of the throttle valve. A fuel passage and an air passage are in communication with the fuel and air mixing chamber. A purge apparatus is in communication with the valve actuation chamber and is operable to move the valve to an open position to open the fuel and air passages to the fuel and air mixing chamber such that a fuel and air mixture may flow from the fuel and air mixing chamber to the fuel and air mixing passage downstream of the throttle valve.

Abstract: A carburetor fuel valve adjustment and limiter assembly for a combustion engine limits the maximum and minimum fuel amounts delivered through the valve of the carburetor. A needle valve of the adjustment and limiter assembly cooperates with a collar and pin generally located axially inward of an enlarged valve head. The collar of the limiter assembly is arranged telescopically with a valve shaft and yieldably biased to lock to the head when moved in an axially outward direction. When locked, and upon rotation of the valve, first and second stops carried by the collar are arranged to bear on a stationary pin carried by a carburetor body. During manufacture, the collar can be pushed axially inward against the bias of a spring to disengage the collar from the head to permit rotation of the needle valve while the collar remains stationary for unlimited adjustment of the needle valve.

Abstract: A fuel-air mixture control apparatus for adjusting the mixture of fuel and air that a carburetor provides to an internal combustion engine. A mixing passage provides a fuel-air mixture to one or more combustion chambers of an internal combustion engine. A main fuel supply passage provides fluid communication between a fuel source and the mixing passage through a main fuel nozzle. An idle fuel supply passage provides fluid communication between a fuel source and the mixing passage through an idle fuel nozzle. An idle fuel ratio control valve adjusts the proportion of fuel drawn into the mixing passage through the idle fuel supply passage to the flow rate of air drawn into the mixing passage. The idle fuel supply passage is in fluid communication with the main fuel nozzle. Vacuum pressure induced by flow rates across the main fuel nozzle, which exceed a predetermined flow rate, precludes idle fuel flow into the mixing passage.

Abstract: A fuel-air mixture control apparatus for adjusting the mixture of fuel and air that a carburetor provides to an internal combustion engine. A mixing passage provides a fuel-air mixture to one or more combustion chambers of an internal combustion engine. A main fuel supply passage provides fluid communication between a fuel source and the mixing passage through a main fuel nozzle. An idle fuel supply passage provides fluid communication between a fuel source and the mixing passage through an idle fuel nozzle. An idle fuel ratio control valve adjusts the proportion of fuel drawn into the mixing passage through the idle fuel supply passage to the flow rate of air drawn into the mixing passage. The idle fuel supply passage is in fluid communication with the main fuel nozzle. Vacuum pressure induced by flow rates across the main fuel nozzle, which exceed a predetermined flow rate, precludes idle fuel flow into the mixing passage.