Abstract: A carburetor for combustion engines, having upstream of an arbitrarily operated throttle valve, an additional throttling element which is controlled automatically by a membrane unit operated by underpressure of vacuum in accordance with air flow. The additional throttling element controls a fuel jet by means of a needle. The discharge location of the fuel jet is at a point where essentially the same underpressure prevails as in the mixing chamber formed between throttle valve and throttling element. In an enrichment system for the heating phase the fuel jet is controlled by a needle whose variable position is determined by the position of a temperature-sensitive element via a lever, and the fuel quantity for acceleration is varied by means of a second membrane unit. The discharge location of this enrichment system is downstream of the throttling element. The second membrane unit may be actuated by underpressure and may have a pressure chamber closed by a movable membrane loaded by a spring.