Abstract: A carburetor for an internal combustion engine comprises a fuel idling circuit opening into the intake pipe downstream of a driver-actuated main throttle. Idle regulation means comprise a first pneumatic element connected to that part of the intake pipe downstream of the main throttle and a second pneumatic element having a movable part connected to the main throttle means by a unidirectional connection such that the throttle means can be opened to an additional extent. The second pneumatic element is subjected to the vacuum in a chamber connected to said part of the intake pipe and also connected to atmosphere by a valve carried by the movable part of the second element and opened by the first pneumatic element moving with respect to the second pneumatic element when there is an increase in the degree of vacuum in the intake pipe.