To provide a method and a device for accurately and assuredly adjusting an air/fuel ratio to a desirable level in a diaphragm carburetor for internal combustion engine.

A diaphragm carburetor for internal combustion engine comprises a choke, a throttle valve, an idle port feeding fuel from a regulating chamber 66, and a main regulating nozzle 64, and automatically adjusts an air/fuel ratio by a solenoid-operated poppet valve 96 or a needle valve and an electronic control circuit. It also incorporates a combined acceleration pump and an idle circuit close mechanism and, in normal running, the throttle shaft to which the main nozzle feeds fuel is operated mechanically so as to assist an automatic electric air/fuel ratio adjusting control. A choke/throttle interlock mechanism also assists the electric air/fuel ratio control or prevents a catalytic converter for exhaust from being damaged. An electric motor gear drive unit is connected to the main regulating needle for fine adjustment, and arrested by itself so as to hold adjusted values. Electronic and mechanical control system parts operated in association with each other have a common box and a main body in a compact total packaging, and intercool electronic and electric parts by flow-in fuel.