Evaporative emissions control system for small internal combustion engines

An evaporative emissions control system (40a, 40b) for small internal combustion engines (28). The system generally includes a charcoal canister (122) and a carburetor (42, 170) with a fuel circuit shutoff valve (80, 222, 240). The charcoal canister is in fluid communication with the air space above the liquid fuel within the engine fuel tank (30), and optionally, with the air space above the liquid fuel within the fuel bowl (58) of a fuel bowl-type carburetor (42). The charcoal canister contains charcoal media (138) 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 (42) or a diaphragm carburetor (170), includes a fuel circuit shutoff valve (80, 222, 240) controlled either by a vacuum signal produced within the engine or by a user-actuated mechanical linkage (36, 238). The fuel circuit shutoff valve closes the fuel circuit (72, 186) 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 (270) is disclosed which contains a minimal amount of fuel when the engine is not running to reduce or eliminate evaporative emissions.