Carburetor fuel supply system

A purge and prime assembly of a carburetor for an engine, comprising:

• a carburetor having a main bore and a fuel metering chamber which in operation supplies fuel to the main bore;
• a purge and prime pump which removes stale fuel and vapor from the carburetor including the fuel metering chamber and draws fresh fuel into the metering chamber before starting the engine;
• a purge and prime passage through which fluid is drawn by the purge and prime pump;
• a return passage through which fluid drawn from the carburetor is discharged from the purge and prime pump;
• a purge valve that prevents fluid from being discharged from the purge and prime pump through the purge passage;
• a return valve that prevents fluid in the return passage from being drawn into the purge and prime pump;
• a priming passage communicating with the purge and prime pump and having an outlet directly communicating with the main bore of the carburetor through which a portion of the fluid discharged from the purge and prime pump is supplied to the main bore;
• a flow restrictor in the priming passage which comprises a sheet of material with a thickness in the direction of fluid flow of less than 0.35 mm and a single hole through the sheet of material having a diameter in the range of 0.05 mm to 0.30 mm and through which all of the priming fluid flows;
• and
• the ratio of flow area of the single hole of the flow restrictor to the minimum effective flow area of the purge passage is between 0.025:1 to 0.2:1.