Abstract: A slidable throttle valve assembly for a carburetor comprising a carburetor body with an intake passage therein, a slidable throttle valve movable across the intake passage, and a throttle valve guide tube connected to the carburetor body and guidably supporting the slidable throttle valve. The carburetor body has guide grooves for guiding the slidable throttle valve which are respectively provided in the body at opposite sides of the intake passage so as to be continuous with the throttle valve guide tube. The throttle valve and guide grooves are of part-circular, cross-sectional shape so that the throttle valve and guide grooves come into contact with each other respectively along lines extending in the sliding direction of the slidable throttle valve downstream of the intake passage.

Abstract: A carburetor adapted to change a rate of fuel flow and an air bleeding characteristic so as to optimize the engine operation irrespective of change in fuel, for example, from gasoline to alcohol or change in altitude. The carburetor includes a main nozzle opening to an intake passage, a fixed support cylinder having a peripheral wall formed therethrough with a plurality of apertures, the peripheral wall being surrounded by an annular chamber communicating with the intake passage upstream of the main nozzle, and an air bleed pipe rotatably fitted in the fixed support cylinder and communicating with the main nozzle and a float chamber. The air bleed pipe has a peripheral wall formed therethrough with a plurality of groups of air bleed ports of different air-bleeding characteristics so that when the pipe is rotated relative to the fixed support cylinder, one group of the air bleed ports are placed into communication with the apertures in the fixed support cylinder so as to change the air bleeding characteristic.