Abstract: A twin air valve carbureter has a single bar which extends diametrically across the two draught tubes upstream thereof, and two air valve flaps which are mounted on opposite sides of the bar, so as to extend across both draught tubes, and are hinged at their ends remote from the bar. Both the flaps co-operate with the bar to define a throat of variable area. The fuel discharge ports are formed in the bar and comprise outwardly-divergent slot ports. A depression responsive fluid pressure motor is linked to each of the flaps to provide compensation for the effect of the reduction of the effective area of each flap as that flap opens. A novel linkage is disclosed for linking a fuel metering needle to one of the flaps.

Abstract: To provide a carburetor in which the fuel/air proportion in the mixture is maintained substantially constant despite variations in atmospheric pressure, supplementary air is supplied to the induction passage downstream of the throttle valve, in a fixed choke carburetor, or to the mixing chamber in an air valve carburetor, the supply of such supplementary air being controlled in accordance with atmospheric pressure.

Abstract: An internal combustion engine cold start device has an air valve which co-operates with a valve seat to vary the cross-sectional area of an auxiliary air supply passage upstream of a plug valve in the passage. The air valve is urged towards the valve seat by coil spring. A fuel metering orifice communicates with the passage between the two valves. The plug valve has a profiled valve member which is linked to a profiled needle which projects into the fuel metering orifice, the needle and the plug valve member being guided for rectilinear movement together along parallel paths to respectively throttle the passage and vary the area of the metering orifice. A coil spring opposes rectilinear movement of the plug valve member and the needle to reduce flow through the passage and the orifice respectivey.