Fuel is delivered through pipe 1 into chamber 2, which contains float 3 operating needle valve 4. From the float chamber, the fuel passes through metering orifices 5 and 6 into the narrow end of venturi 7 where the fuel-air mixture is formed. At the moment of starting, the fuel-air mixture must be enriched. This is accomplished by the provision of choke 8 in air supply pipe 10 and additional needle valve 9. Rigidly mounted on the shaft of choke 8 is cam 11 which is rigidly attached to control lever 12. In starting, lever 12 is turned to close choke 8, cam 11 turns lever 13 to raise needle valve 9. This enriches the fuel-air mixture because additional fuel is admitted into venturi 7 through valve 9 and passages a and d. Automatic valve 14 is mounted on choke 8. As soon as the engine starts running, the vacuum acting on the choke is sharply increased and valve 14 is withdrawn from the choke, opening holes b in the choke. This admits additional air into the venturi and cuts down enrichment of the mixture. As the engine heats up, the choke is gradually opened, closing needle valve 9 and leaning the fuel-air mixture.
$3988$LHP,FD$