Abstract: A carburetor has an apparatus for compensation of idling revolution of an internal combustion engine. The apparatus comprises a bypass passage one end of which is opened to the air suction conduit of the carburetor upstream of a throttle valve, the other end opened to the same downstream of the throttle valve. A fuel passage supplies fuel into the bypass passage to form a fuel-air mixture, a solenoid valve provided on the bypass passage for controlling a quantity of the fuel-air mixture in response to operation of a load such as, for example, heater, a radiator fan, lights, an air conditioner, etc. so that the idling rotational speed to be decreased by such operations is compensated by supplying fuel-air mixture into the air suction conduit.

Abstract: An adjustment prevention mechanism comprises a stationary covering member disposed opposite to a head of an adjusting screw for adjusting fuel flowing in a slow speed fuel passage in idling of an engine, and a cap-shaped plug. The stationary covering member is secured to something within an engine room, for example a suction pipe of the engine, and has a hole through which the adjusting screw is adjusted. The cap-shaped plug is inserted rigidly in the hole to blockage the hole after the adjusting screw was adjusted, so that the adjusting screw can not be readjusted by usual users after the engine is transferred to the users.