intake valve 16 the sub intake passages 37 are of substantially less cross sectional area than the main intake passages 15 so that a given mass flow through these passages will enter the chambers 14 at a substantially higher velocity if desired the sub intakes passages 37 and ports 38 may be directed so as to also impart a swirl to the intake charge in addition to the idle and low speed circuit 31 the carburetor barrel 18 is provided with a main fuel discharge including a boost nozzle 39 a similar main fuel discharge is also provided in the carburetor barrel 19 which serves the chamber adjacent the chamber 14 shown in fig1 a choke valve 41 is rotatably supported upon a shaft 42 in only the carburetor barrel 18 upstream of the venturi 24 and boost nozzle 39 as is known the choke valve 41 provides cold starting enrichment and as will become apparent this cold starting enrichment serves all of the chambers fed by the sub intake passages 33 36 and 37 thus only one carburetor barrel need be provided with a cold starting enrichment device as described in the aforenoted copending application ser no 838 353 the linkage system for controlling the operation of the main throttle valve 23 and the sub throttle valve 34 will now be described by particular reference to fig3 a bellcrank 43 is affixed to the throttle valve shaft 25 and has arms 44.