Membrane carburetor for a portable handheld work apparatus

A membrane carburetor for an internal combustion engine in a portable handheld work apparatus including a motor-driven chain saw, cutoff machine and brushcutter, the membrane carburetor comprising:

• a carburetor housing defining an intake channel communicating with the engine and through which a stream of combustion air flowing in an intake flow direction is drawn by suction when the engine is operating;
• said intake channel defining a venturi section;
• a throttle flap pivotally mounted in said intake channel downstream of said venturi section;
• said carburetor housing further defining an interior space;
• a control membrane mounted in said interior space so as to define a control chamber therein bounded by said membrane;
• fuel supply means for supplying fuel to said control chamber;
• a main nozzle for metering fuel from said control chamber and said main nozzle opening into said intake channel in the region of said venturi section;
• said fuel supply means including a control valve for controlling the inflow of said fuel to said control chamber;
• said control membrane being operatively connected to said control valve for actuating said control valve;
• said main nozzle having an outlet cross section through which the fuel passes when entering said intake channel;
• said main nozzle having a check valve defining a valve chamber through which fuel passes as the fuel flows to said outlet cross section;
• said check valve including a valve seat in said valve chamber and a valve platelet coacting with said valve seat to open and close said check valve;
• and,
• a sieve platelet disposed downstream of said valve seat and said valve platelet and arranged so as to substantially completely cover said outlet cross section.