twin-choke downdraught carburetor Possible demonstrations: throttle butterflies open simultaneously function of choke butterflies, throttle butterflies, float with valve needle, pull-down device, accelerator pump and idle- speed stop description ordernumber 1029 see also: exhaust gas recirculation valve I nozzle holder with two-spring injection nozzle and needle-displacement sensor pump with slide-valve control (electronically controlled) valve timing model case