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The authors developed a simple simulation method of motorcycle emission mode, using a popular chart calculation software for a personal computer, to calculate from the motorcycle's various specifications and the engine bench test data. The precision or verification by a mass production model was of a sufficiently good level. This simple simulation method was easy to use and effective in reducing the research period. Moreover, the experimental motorcycle (Scooter, Two-stroke, 50cm3) that adopted the stratified combustion system for a fuel economy improvement and CO2 reduction, was made and experimented on the ECE40 mode as a sample case. Approximately 20 % of fuel economy improvement and CO2 reduction were achieved and the estimation was effectively proved.

This emission reduction technique has been researched on motorcycles equipped with a four-cylinder, liquid-cooled engine of 1100cm3 displacement in order to comply with the EURO-3 emission regulation. The EURO-3 emission regulation will be enforced in Europe beginning in year 2006. Compared to the EURO-2 regulation, reduction of cold-start HC and reduction of NOx from the extra-urban driving cycle are the main issues for EURO-3 compliance. The hydrocarbon reduction during cold-starting was achieved by the method of early catalyst activation using a combination of an Idle Air Control Valve system (IACV), ignition-retard, and atomization of fuel spray. In the extra-urban driving cycle, the fine controlled air-fuel ratio reduced. In addition, optimization of the number of three-way catalyst cells and their capacity also reduced NOx. Moreover, power loss decline caused by increased exhaust resistance due to increasing the catalyst size was avoided by optimizing the catalyst location.

Amidst the growing concerns for the global environment and the escalating demands for low exhaust emissions and high fuel economy small motorcycles, the electronically controlled fuel injection system (hereafter referred to as FI system) is making its appearance as an effective device to reduce emissions while improving fuel economy by precisely controlling the air-to-fuel ratio. Fuel injectors and fuel pumps currently used in small motorcycle FI systems were originally derived from multi-cylinder engine automobile and large motorcycle FI system components, and therefore have not been necessarily suitable for small motorcycle application.