This paper introduces a control system combining both electronics and mechanics to supply the proper air/fuel ratio required by the engine at the wide speed range and load range. This upgraded control system results in better combustion and an overall improvement in engine performance.Motorcycles adopt reasonable carburetors for fuel control in cost and functions, while the fuel injection device is scarecely used under cost cosideration. The caburetors can not sufficiently control the air/fuel ratio required by the engine from low to high engine speed. And they make rich fuel areas and lean areas.For that reason, electronically-controlled motorcycle carburetors revise these areas and we have tried to supply more ideal air/fuel ratio at wide range of engine speed. At the rich fuel area, the duty solenoid operated by control unit supplies the most suitable air/fuel ratio with correcting air mass. In acceleration, first, the throttle sensor detects throttle opening acceleration, and the carburetor increases air flow quantity. Consequently the system creates the best air/fuel ratio. These controls must generate a good throttle response to motorcycle riders.