Variable venturi carburetor

In a prior-art variable venturi carburetor in which the cross-sectional area of venturi is automatically varied according to the amount of intake air to keep the flow rate of intake air or the vacuum generated at the venturi at a constant level, since the cross section of venturi changes rectangularly, fuel is concentratedly jetted only near the middle portion of the venturi, so that fuel is not uniformly mixed with air passing through the venturi. To overcome these drawbacks, a wall having a reverse trapezoidal recess is provided near the nozzle and further a pair of triangular slots or cutouts are formed near the lower end surface of the suction piston obliquely and symmetrically so as to slidably engage with the wall, with the result that the cross section of the venturi changes trapezoidally and therefore a stable mixture is obtained even when the engine is running at a low speed or being idled.