Importance

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Abstract

The apparatus prevents fuel vapor from being discharged to an intake passage from a fuel metering chamber of a carburetor and maintains a substantially constant fuel pressure in the fuel metering chamber so as to stabilize the amount of the fuel discharged to the intake passage. The pump has a drive force produced by a pulsation pressure generated in a crank chamber of an engine or an intake tube. A discharge chamber of a fuel pump and a fuel tank are connected by a relief passage, and the relief passage is provided with a pressure regulating valve discharging a pressure equal to or greater than a set pressure in the discharge chamber to the fuel tank. Fuel vapor is prevented from being generated in an inner portion of a fuel metering chamber and the amount of fuel discharged to an intake passage is stabilized, by discharging a part of the fuel at a time when a pump discharge fuel pressure is high to the fuel tank together with the fuel vapor generated in the fuel pump, and only feeding the fuel at the set pressure to the fuel metering chamber. Further, because the fuel having a comparatively low temperature is circulated in the fuel pump and within the fuel tank by discharging excess fuel to the fuel tank, the carburetor is cooled, and the generation of fuel vapor is inhibited.

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First Claim