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A new control system using O₂ feedback control has been developed as an alternative to intake air pressure sensors. This control method uses the operational condition compensation coefficient Kbu. This coefficient encompasses the state of the engine and environmental conditions such as atmospheric pressure, and corrects fuel injection in response to changes in these factors. Kbu makes it possible to control the amount of fuel injection without depending on an intake air pressure sensor. It also makes it possible to carry out the appropriate air-fuel ratio correction even at times when O₂ feedback control is not operating, such as the cold period, when the engine is first started, or during transient operation, by using Kbu values recorded in the Engine Control Unit (henceforth ECU).

The idling stop system for scooters employs an ACG starter connected directly to the crankshaft without reduction gears; therefore, it is possible to start the engine silently. The system is designed to stop the engine automatically when the scooter stops, and the engine restarts simply by opening the throttle. Scooters with 50 cm₃ engines have already been employing the idling stop system. This system for 125 cm₃ engines was developed to enlarge the application range of the idling stop system. It needs a large ACG starter because the cranking torque is higher than that of 50 cm₃ engines, so the cranking torque was reduced by using a decompression device. The ACG starter was designed with a thin and large diameter construction in order to minimize the increase in engine width. The new idling stop system was developed with an integrated control of the fuel injection system and the ACG starter.