To optimize setting of a fuel discharge amount in a low opening range of a rotary throttle valve, and to widen a range of engine characteristics.
A rotary throttle valve type carburetor 1 comprises: an intake passage 3; a rotary throttle valve 5 opening/closing the intake passage; a fueling nozzle 7 projecting and inserted upward in a venturi hole 6 of the rotary throttle valve; a needle 8 for fuel gauging hanging in the venturi hole of the rotary throttle valve and inserted into the fueling nozzle. In the carburetor 1, a fuel discharge passage 23 having a portion whose cross section is gradually increases upward is formed in an inner face of one side part of a peripheral wall of the fueling nozzle. Since the tip of the needle fits to the part with cross section of the fuel discharge passage gradually increasing in a range of slight lift amount of the needle, change in cross section of the passage along with vertical motion of the needle becomes slow.
MICHIYAMA YOSHIAKI
OKANE SHINICHI
TOBIUCHI TERUHIKO
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