Carburetor with deceleration circuit

Claim 1

A carburetor for an internal combustion engine comprising a carburetor body, a carburetor induction passage formed in said carburetor body, a venturi in said carburetor induction passage, a throttle valve operatively disposed in said carburetor induction passage, a main mixture circuit opening into said venturi in said carburetor induction passage for supplying an air-fuel mixture to said carburetor induction passage for highspeed and acceleration operations of said engine, an idling and slow-running mixture circuit opening into said carburetor induction passage downstream of said throttle valve for supplying an air-fuel mixture to said carburetor induction passage for lowspeed and deceleration operations of said engine, a float chamber which supplies fuel to said two circuits, a by-pass passage having an inlet port communicating with said carburetor induction passage upstream of said venturi and an outlet port comunicating with said carburetor induction passage downstream of said throttle valve, an air jet provided in said by-pass passage to control the flow rate of air passing therethrough, a fuel jet provided in a fuel supply by-pass passage opening to the first mentioned by-pass passage downstream of said air jet and leading directly from said float chamber, and a control unit for controlling the flow of air-fuel mixture passing through the first mentioned by-pass passage in response to the vacuum prevailing in said carburetor induction passage downstream of said throttle valve, said control unit including a housing having first and second vacuum chambers and a spring seat intervening therebetween said spring seat having formed therin a central aperture, said second vacuum chamber provided with a port communicating with said carburetor induction passage upstream of said venturi through a calibrated air bleed, a passage having one end communicating with said carburetor induction passage downstream of said throttle valve and the other end communicating with said first vacuum chamber, a cap member attached to one end of said housing and having an opening vented to the atmosphere, a first diaphragm member interposed between said one end of said housing and said cap member, a first atmosphere chamber formed between said first diaphragm member and the inner surface of said cap member, a control valve element connected to said first diaphragm member and extending through said central aperture formed in said spring seat to control communication between said first and second vacuum chambers, a first compression spring disposed in said first vacuum chamber for biasing said first diaphragm member in a direction to cause said control valve element to close said central aperture of said spring seat for thereby interrupting communication between said first and second vacuum chambers, a second diaphragm member interposed between the other end of said housing and said carburetor body, a second atmospheric chamber defined in a cavity formed in said carburetor body and said second diaphragm member, said second atmospheric chamber communicating with said carburetor induction passage upstream of said venturi, means defining an orifice between said second atmospheric chamber and said passage having one end communicating with said induction passage downstream of said throttle valve, an adjusting valve element connected to said second diaphragm member and extending through an opening formed in said carburetor body into said by-pass passage to open and close said by-pass passage, and a second compression spring disposed in said second vacuum chamber for biasing said second diaphragm member in a direction to cause said adjusting valve element to close said by-pass passage, said first vacuum chamber being subjected to the vacuum prevailing in said carburetor induction passage downstream of said throttle valve, whereby when the vacuum in said first vacuum chamber exceeds a predetermined value during deceleration operation of said engine, said first diaphragm member is moved against the force of said first compression spring in a direction to cause said control valve element to open said central aperture formed in said spring seat for interconnecting said first vacuum chamber with said second vacuum chamber to permit the vacuum to act on and cause said second diaphragm member to move against the force of said second compression spring in a direction to cause said adjusting valve element to open said by-pass passage.