Carburetor

A carburetor comprising:

• a manual choke valve;
• a bypass air passage for connecting an upstream side and a downstream side of the choke valve and supplying air during engine start-up before warm-up when the choke valve is closed;
• and
• air flow volume adjusting means for adjusting the air flow of the bypass air passage in accordance with a temperature condition, wherein:
• the air flow volume adjusting means has a cylindrical valve hole provided partway along said bypass air passage, and a piston-shaped open-close valve that slides reciprocatingly inside the valve hole to open and close said bypass air passage;
• a proximal end side of the open-close valve is pressed by an urging means, and a distal end side is in continuous contact with a side face of a choke valve shaft while being urged and caused to slide by said side face so that the distance from a central axis of said choke valve shaft varies in accordance with an angle of rotation of said choke valve shaft;
• a projecting part that projects from and recedes into the distal end of a body of said open-close valve is urged by an elastic body to allow the length in the direction of sliding to vary in an elastic fashion so that the distal end face is continuously pressed against said side face;
• said urging means comprises a temperature-sensitive material, and elongates in the direction of sliding at or above a prescribed set temperature;
• and
• when said choke valve is fully open, said bypass air passage is closed by said open-close valve;
• when said choke valve is closed and in the case when the ambient temperature is lower than said prescribed temperature, said projecting part projects while said body is kept in a closed valve position without said urging means elongating, and said bypass air passage is put into a closed state;
• and when said choke valve is closed when the ambient temperature is at or above said prescribed temperature, said urging means elongates and said body is put into an open valve position while said projecting part is caused to recede, and said bypass air passage is put into an open state.