PURPOSE: To make negative pressure act in a direction of drawing fuel in a throw jet or suchlike, as well as to improve the extent of speed persistence with a fuel feed function at time of engine low speed increased, by opening an air intake of a fuel increaser to an air chamber for air jet use.
CONSTITUTION: With engine starting, fuel in a float chamber 40 is fed to an intake passage 32 of a carburetor 24 from a main jet and a throw jet 44. At this time, since a heater 68 of a fuel increaser 52 is not energized with current, a valve body 64 is opened upward. Then, a diaphragm 53 of the fuel increaser 52 is operated, and the fuel in the float chamber 40 is guided to a pump case 54 from an outlet 57 and then it passes through the circumference of a needle valve 62 and is discharged to another outlet 82. In this case, negative pressure being produced in an intake manifold 22 is transferred to an air chamber 74 via an increment fuel passage 84, the fuel increaser 52 and air passages 71, 72. Since it works in a direction of drawing the fuel from the throw jet 44, the fuel being supplied at time of low speed becomes somewhat thickish.
OKAZAKI MASAKI
HASEGAWA JUNICHI