Abstract: A carburetor equipped with an auto-choke device is disclosed wherein according to one embodiment a leak valve is disposed in a negative pressure chamber of a diaphragm device adapted to operate by a negative pressure in a suction passage downstream of a throttle valve so as to open a choke valve in said suction passage to a predetermined degree of opening (complete explosion opening) after an engine has rotated by itself, and when the diaphragm has executed a predetermined shift, the leak valve is opened, and simultaneously, the downstream of the leak valve is brought into the atmospheric pressure for engine temperatures below a set value and into the same negative pressure as that of the negative pressure chamber for engine temperatures at and above the set value, whereby the operating stroke of the diaphragm is changed-over in two stages in dependence upon the water temperature or oil temperature, and the complete explosion opening of the choke valve is changed-over in two stages so that it may become narro

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.