PURPOSE: To set and optimize the maximum fuel supply quantity by connecting fixed throttles to a main nozzle and an idling chamber at the downstream end and providing an adjustable throttle for reducing the entire flow cross section up to a pregiven minimum value.

CONSTITUTION: A throttle valve 4 arranged in an intake duct 2 and a main nozzle 23 communicating with the intake duct 2 in front of the throttle valve 4 in the flow direction 6 of intake air are provided. The maximum flow cross section for fuel supply, in particular, is pregiven by at least one fixed throttle 25, 28. The fixed throttles 25, 28 are connected to the main nozzle 23 and an idling chamber 30 at the downstream end. An adjustable throttle 27 is provided for reducing the entire flow cross section up to a pregiven minimum value. Thus, the maximum fuel supply quantity can be set without the need for a special test in a factory and the fuel supply quantity can be suitably optimized by an operator.