Internally vented float bowl carburetor having a cold start vent conduit

A carburetor for providing a fuel/air mixture to an internal combustion engine, comprising:

• a carburetor body having a bore formed therein, sid bore including an air inlet passage having an air inlet opening defining a fuel/air mixture passage, wherein a vacuum condition exists in said bore upon engine operation;
• a float-regulated fuel supply bowl adapted to contain a quantity of liquid fuel and having a headspace above said fuel;
• a fuel nozzle for conveying fuel from said fuel supply bowl to said fuel/air mixture passage;
• a vent passageway for venting excess pressure from said headspace to said bore;
• and
• thermally-actuated bowl venting means for overriding the venting effect of said vent passageway while the temperature of the engine is less than a given temperature, wherein said bowl venting means ceases to override the venting effect of said vent passageway upon the attainment of said given temperature.

A carburetor for providing a fuel/air mixture to an internal combustion engine, comprising:

• a carburetor body having a bore formed therein, said bore including an air inlet passage having an air inlet opening defining a fuel/air mixture passage, wherein a vacuum condition exists in said bore upon engine operation;
• a float-regulated fuel supply bowl adapted to contain a quantity of liquid fuel and having a headspace above said fuel;
• a fuel nozzle for conveying fuel from said fuel supply bowl to said fuel/air mixture passage;
• an internal vent passageway for providing air communication between said headspace and said bore;
• an external vent passageway extending from said headspace to the atmosphere external of the carburetor;
• a first thermally-actuated valve in said internal vent passageway, said valve being in a closed position while the temperature of the engine is less than a first given temperature, thereby preventing said headspace to be in communication with said bore, said first valve being moved to an open position upon attainment of said first given temperature, thereby permitting said headspace to be in communication with said bore;
• and
• a second thermally-actuated valve in said external vent passageway, said valve being in an open position while the temperature of the engine is less than a second given temperature, thereby permitting said headspace to be in direct communication with the atmosphere, said valve being moved to a closed position upon the attainment of said second given temperature, thereby preventing said headspace to be in direct communication with the atmosphere.

An internal combustion engine comprising:

• a crankcase including a metal cowling;
• a cylinder in said crankcase;
• a carburetor for providing a fuel/air mixture to the cylinder, said carburetor comprising a carburetor body having a bore formed therein, said bore including an air inlet passage having an air inlet opening defining a fuel/air mixture passage, wherein a vacuum condition exists in said bore upon engine operation, said carburetor further including a float regulated fuel supply bowl adapted to contain a quantity of liquid fuel having a headspace above said fuel and a fuel nozzle for conveying fuel from said fuel supply bowl to said fuel/air mixture passage;
• an external vent passageway extending from said headspace to the atmosphere external of the carburetor;
• a thermally actuated valve attached to said metal cowling;
• a flexible tube extending from said external vent passageway to said valve, said tube having a tubular passageway in air communication with said external vent passageway and a conduit in said valve;
• wherein said valve is in an open position while the temperature of the metal cowling is less than a given temperature, thereby permitting said headspace to be in direct communication with the atmosphere, and said valve is in a closed position upon the attainment of said given temperature, thereby preventing said headspace to be in direct communication with the atmosphere.