Abstract: An acceleration pump delivers additional fuel to both the main intake passage and the auxiliary intake passage of an internal combustion engine, to facilitate cold starting. In such an engine, each main combustion chamber is in communication with an auxiliary combustion chamber, respectively. Coordinated means are provided for operating said acceleration pump and throttle valves in said intake passages. Communication between the acceleration pump and the main intake passage remains open at all times, but a passageway connecting the acceleration pump and the auxiliary intake passage is closed except when the ambient temperature is low. Closure of the connecting passageway is effected automatically or in coordination with operation of the choke valve for the main intake passage.