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An evaporative emissions control system for small internal combustion engines. The system generally includes a charcoal canister and a carburetor with a fuel circuit shutoff valve. The charcoal canister is in fluid communication with the air space above the liquid fuel within the engine fuel tank, a

An evaporative emissions control system for small internal combustion engines. The system generally includes a charcoal canister and a carburetor with a fuel circuit shutoff valve. The charcoal canister is in fluid communication with the air space above the liquid fuel within the engine fuel tank, and optionally, with the air space above the liquid fuel within the fuel bowl of a fuel bowl-type carburetor. The charcoal canister contains charcoal media which absorbs fuel vapors when the engine is not running. During running of the engine, vacuum within the carburetor induces a flow of atmospheric air through the charcoal canister to purge the collected fuel vapors from the charcoal media, and the fuel vapors pass into the engine for consumption. The carburetor of the engine, which may be either a fuel bowl-type carburetor or a diaphragm carburetor, includes a fuel circuit shutoff valve controlled either by a vacuum signal produced within the engine or by a user-actuated mechanical linkage. The fuel circuit shutoff valve closes the fuel circuit of the carburetor upon engine shutdown to prevent escape of fuel vapors from the carburetor to the atmosphere. In another embodiment, a weir-type carburetor is disclosed which contains a minimal amount of fuel when the engine is not running to reduce or eliminate evaporative emissions.

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What is claimed is: 1. An internal combustion engine, comprising: a fuel tank containing liquid fuel; a fuel vapor control device including a housing in fluid communication with an upper portion of said fuel tank, said housing containing fuel vapor absorbent media, whereby fuel vapors from the liqu

What is claimed is: 1. An internal combustion engine, comprising: a fuel tank containing liquid fuel; a fuel vapor control device including a housing in fluid communication with an upper portion of said fuel tank, said housing containing fuel vapor absorbent media, whereby fuel vapors from the liquid fuel within said fuel tank are trapped by said absorbent media; and a carburetor, comprising: a carburetor body having an air intake passage including a venturi portion; a fuel chamber containing liquid fuel, said fuel chamber in fluid communication with said fuel tank; a main fuel circuit fluidly communicating said fuel chamber with said venturi portion of said air intake passage; an idle fuel circuit fluidly communicating said fuel chamber with said air intake passage downstream of said venturi portion; and a fuel circuit shutoff valve disposed upstream of said main and idle fuel circuits, including a valve member movable between a first, closed position in which fuel flow from said fuel chamber to said air intake passage through said main and idle circuits is substantially prevented and a second, open position in which fuel flow from said fuel chamber to said air intake passage through said main and idle fuel circuits is allowed. 2. The engine of claim 1, wherein said fuel chamber of said carburetor is a fuel bowl, said fuel bowl including a fuel inlet valve metering fuel into said fuel bowl from said fuel tank. 3. The engine of claim 2, wherein said housing is in fluid communication with an upper portion of said fuel bowl, whereby fuel vapors from said fuel bowl are trapped by said absorbent media within said housing. 4. The engine of claim 1, wherein said valve member of said fuel circuit shutoff valve is normally disposed in said first, closed position, and is movable to said second, open position responsive to vacuum with said engine. 5. The engine of claim 4, wherein said fuel circuit shutoff valve further comprises a biasing member biasing said valve member toward said first, closed position. 6. The engine of claim 4, wherein said carburetor comprises: a valve housing including a diaphragm coupled to said valve member; a vacuum chamber defined between said diaphragm and said housing and in fluid communication with said air intake passage of said carburetor, wherein vacuum generated within said air intake passage upon running of said engine is communicated to said vacuum chamber to move said diaphragm and said valve member to said second, open position. 7. The engine of claim 4, wherein said carburetor comprises: first and second diaphragms each connected to said valve member of said fuel circuit shutoff valve, said fuel chamber defined between said first diaphragm and said carburetor body; a vacuum chamber defined within said carburetor body between said first and second diaphragms, said vacuum chamber in fluid communication with said air intake passage, said first and second diaphragms and said valve member together movable responsive to vacuum within said vacuum chamber between a first position corresponding to engine shutdown in which said vacuum chamber is at atmospheric pressure and said valve member blocks fuel flow from said fuel chamber to said fuel circuit, and a second position corresponding to running of the engine in which said vacuum chamber is at sub-atmospheric pressure said valve member allows fuel flow from said fuel chamber to said fuel circuit. 8. The engine of claim 4, wherein said air intake passage further includes a throttle valve downstream of said venturi portion, and said fuel circuit shutoff valve is movable to said second, open position responsive to a vacuum signal from the air intake passage downstream of said throttle valve. 9. An internal combustion engine, comprising: a fuel tank containing liquid fuel; a fuel vapor control device including a housing in fluid communication with an upper portion of said fuel tank, said housing containing fuel vapor absorbent media, whereby fuel vapors from the liquid fuel within said fuel tank are trapped by said absorbent media; and a carburetor, comprising: a carburetor body having an air intake passage; a fuel chamber containing liquid fuel, said fuel chamber in fluid communication with said fuel tank; a fuel circuit fluidly communicating said fuel chamber with said air intake passage, and a fuel circuit shutoff valve associated with said fuel circuit, including a valve member movable between a first, closed position in which fuel flow from said fuel chamber to said air intake passage is substantially prevented and a second, open position in which fuel flow from said fuel chamber to said air intake passage is allowed, said fuel circuit shutoff valve further comprising: an operator-controlled member; and mechanical linkage connecting said operator-controlled member to said fuel circuit shutoff valve, whereby said fuel circuit shutoff valve is manually controlled. 10. An internal combustion engine, comprising: a fuel tank containing liquid fuel; and a carburetor, comprising: a carburetor body having an air intake passage therethrough, said air intake passage including a venturi portion; a fuel bowl disposed beneath said carburetor body, said fuel bowl in fluid communication with said fuel tank; a main fuel circuit fluidly communicating said fuel bowl with said venturi portion of said air intake passage; an idle fuel circuit fluidly communicating said fuel chamber with said air intake passage downstream of said venturi portion; and a vacuum-actuated fuel circuit shutoff valve disposed upstream of said main and idle fuel circuits and including a vacuum chamber in fluid communication with said air intake passage, a diaphragm disposed within said vacuum chamber and connected to a valve member, said diaphragm and valve member together movable between a first, closed position corresponding to atmospheric pressure in said vacuum chamber in which fuel flow from said fuel chamber to said air intake passage through said main and idle fuel circuits is substantially prevented and a second, open position corresponding to sub-atmospheric pressure in said vacuum chamber in which fuel flow from said fuel chamber to said air intake passage through said main and idle fuel circuits is allowed. 11. The internal combustion engine of claim 10, further comprising a fuel vapor control device including a housing in fluid communication with an upper portion of said fuel tank, said housing containing fuel vapor absorbent media, whereby fuel vapors from the liquid fuel within said fuel tank are trapped by said absorbent media. 12. The internal combustion engine of claim 10, further comprising a fuel vapor control device including a housing in fluid communication with an upper portion of said fuel bowl, said housing containing fuel vapor absorbent media, whereby fuel vapors from the liquid fuel within said fuel bowl are trapped by said absorbent media. 13. The internal combustion engine of claim 10, wherein said air intake passage further includes a throttle valve downstream of said venturi portion, and said fuel circuit shutoff valve is movable to said second, open position responsive to a vacuum signal from the air intake passage downstream of said throttle valve. 14. An internal combustion engine, comprising: a fuel tank containing liquid fuel; and a carburetor, comprising: a carburetor body having an air intake passage therethrough; first and second diaphragms; a fuel chamber defined between said first diaphragm and said carburetor body, said fuel chamber in fluid communication with said fuel tank; a fuel circuit fluidly communicating said fuel chamber with said air intake passage; a vacuum chamber defined within said carburetor body between said first and second diaphragms, said vacuum chamber in airflow communication with said air intake passage; and a fuel circuit shutoff valve including a valve member connecting said first and second diaphragms, said first and second diaphragms together movable with said valve member responsive to vacuum within said vacuum chamber between a first position corresponding to atmospheric pressure in said vacuum chamber, in which said valve member closes said fuel circuit, and a second position corresponding to sub-atmospheric pressure within said vacuum chamber, in which said valve member opens said fuel circuit. 15. The internal combustion engine of claim 14, further comprising a fuel vapor control device including a housing in fluid communication with an upper portion of said fuel tank, said housing containing fuel vapor absorbent media, whereby fuel vapors from the liquid fuel within said fuel tank are trapped by said absorbent media. 16. An internal combustion engine, comprising: a fuel tank containing liquid fuel; a fuel vapor control device including a housing in fluid communication with an upper portion of said fuel tank, said housing containing fuel vapor absorbent media, whereby fuel vapors from the liquid fuel within said fuel tank are trapped by said absorbent media; and a carburetor, comprising: a carburetor body having an air intake passage; a fuel chamber having a fuel inlet and a fuel outlet each in fluid communication with said fuel tank; a fuel circuit fluidly communicating said fuel chamber with said air intake passage; and a weir disposed within said fuel chamber, said fuel circuit and said fuel inlet each in fluid communication with said weir; and a fuel pump driven from said engine, said fuel pump circulating fuel from said fuel tank to said chamber and thence from said chamber to said fuel tank. 17. The engine of claim 16, wherein said weir further comprises an open upper end in fluid communication with said fuel chamber. 18. The engine of claim 16, wherein said weir further comprises a bleed hole in a lower portion thereof, said bleed hole in fluid communication with said fuel chamber. 19. The engine of claim 16, further comprising at least one of: a fuel inlet check valve disposed between said fuel pump and said fuel inlet; and a fuel outlet check valve disposed between said fuel outlet and said fuel tank. 20. The engine of claim 16, wherein said housing is in fluid communication with an upper portion of said fuel chamber, whereby fuel vapors from said fuel chamber are trapped by said absorbent media within said housing.