at slide supporting portions 17 the slide supporting portion is provided with a pair of facing grooves 18 and a connecting bottom groove 19 open to the carburetor throat which is indicated at 21 a throttle slide generally indicated at 22 is mounted in these grooves and is vertically adjustable to vary the unblocked portion of throat 21 the width of slide 22 is slightly greater than that of intermediate portion throat 21 and the slide has a generally rectangular shape as seen partially in fig2 a concave arcuate recess 23 is centrally formed along the lower or control edge of slide 22 means not shown is provided for limiting the downward movement of slide 22 thus defining the idle position this position may be chosen so that a slight gap 24 exists between the central portion of recess 23 and the bottom of throat 21 alternatively for purposes such as racing the setting may be for complete shutoff at idle the recess 23 being within slot 19 slide 22 is quite thin but has a central enlargement 25 on its downstream side which extends from the top of the slide toward recess 23 means shown more particularly in the aforementioned copending application is provided for vertically adjusting slide 22 bowl 14 is provided with a fuel inlet passage 26 leading to a float needle valve generally indicated at 27 this valve is controlled by a pair of floats 28 and 29 guided by pins 31 within the bowl the arrangement is such that floats 28 and 29 when lifted by the rising level of fuel in bowl 14 will close valve 27 thus controlling the level of fuel in the bowl a fuel discharge nozzle tube 32 extends downwardly from the lower portion of body 12.