Abstract
Concerns about environmental protection and energy saving are growing in the world, and Thailand market also strongly requires an improvement of fuel consumption and emission for motorcycles. Therefore, we developed a 125cm3 4-stroke engine with revolutionized fuel consumption and emission for the Thailand market. For enhancing the fuel consumption, the friction of contact surfaces of therocker arm and piston and the mechanical input of the generator was reduced. Also the combustion efficiency was enhanced by changing the ignition timing by throttle opening. For reducing the emission, the secondary air pulse induction system, introducing fresh air into an exhaust port, was employed. As a result, the fuel consumption was enhanced 30% in ECE40 mode compared to the 108cm3 engine of the previous model. The emission was reduced 55% for CO and 60% for HC+NOx to the 4th emission regulation value in Thailand.