Air-fuel ratio control device for a carburetor

Abstract

It is intended to provide an air-fuel ratio control device for a carburetor, which is capable of variably inject fuel by opening and closing a choke valve in accordance with an opening degree of a throttle valve and the load and which is capable of achieving low cost, clean emission and fuel saving by attaining a desired air-fuel ratio in an entire operational range (rotation speed, load) of the internal combustion engine. The air-fuel ratio control device is provided with, but not limited to, a choke valvearranged in an intake path of an internal combustion engine, a throttle valvearranged in the intake path on a downstream side of the choke valve, a first stepper motordriving the choke valveto adjust an opening degree of the choke valve, a second stepper motordriving the throttle valveto adjust an opening degree of the throttle valve, and a controllercontrolling the opening degree of the choke valvein accordance with a change of a rotation speed of the internal combustion enginebased on the opening degree of the throttle valve, and, when the rotation speed of the internal combustion engineis constant, controls the opening degree of the choke valvebased on a map which determines the opening degree of the choke valvefrom load of the internal combustion engine, so as to achieve a desired air-fuel ratio.