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 orifice 5 into the narrow end of venturi 6 where it is mixed with air entering at increased pressure through metering orifice 19. The mixture strength can be varied by varying the relative positions of the throttle valve and choke. Rigidly mounted on the choke shaft are levers 9 and 10 which are attached to each other. Lever 9 is the control lever. Lever 10 is linked by tie-rod 11 to lever 12 which is rigidly secured to cam 13. The position of throttle valve 14 depends upon the setting of screw 15 which contacts cam 13. In starting, choke 8 is closed by means of tie-rod 16, turning lever 10 counterclockwise so that tie-rod 11 turns cam 13. This slightly opens throttle valve 14. As soon as the engine starts running, the vacuum behind the choke is sharply increased and valve 18 is withdrawn from the choke, opening holes provided in the choke. This admits additional air into the venturi and cuts down enrichment of the mixture. As the engine heats up the throttle valve is gradually opened. This can be done by means of tie-rod 17.
$3989$LHP,FD$