PURPOSE: To provice a speed regulator for carburetor which reduces control man-hour for obtaining low speed air quantity, and improves the development efficiency of a carburetor, and moreover has high durability against foreign matter.
CONSTITUTION: A low speed air regulating screw 41 is arranged in a low speed air passage 40 toward a low speed mixing pipe 9. The low speed air passage 40A located on a side more upstream than the low speed air regulating screw 41 branches off into the first and the second low speed air passage 43, 43. The first air jet 44 is arranged in the first low speed air passage 42. A normally open type opening and closing valve V which closes the second low speed air passage 43 in the case where negative pressure in a suction passage 2A on the side from the throttle valve 8 toward an engine rises more than a fixed value is arranged in the second low speed air passage 43.
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