<![CDATA[Motorcycle exhaust emissions depend on combustion quality, fuel properties, engine speed, and exhaust-system characteristics. This study compared carbon monoxide (CO), hydrocarbons (HC), and carbon dioxide (CO₂) from a 150 cc fuel-injected motorcycle using Pertamax RON 92 with a standard exhaust and a straight-through racing exhaust. An experimental design was applied at 1500, 2000, and 2500 rpm. Emissions were measured with an NHA-506 gas analyzer after the engine reached operating temperature, and each condition was repeated three times. The standard exhaust produced a relatively stable emission pattern across the tested speeds. The racing exhaust produced higher CO and HC at 1500 rpm, but its best performance occurred at 2000 rpm, where CO decreased to 1.76%, HC to 80 ppm, and CO₂ increased to 12.4%. Relative to the standard exhaust at the same speed, CO and HC were lower by 64.6% and 53.8%, respectively. The combustion and reaction-kinetics interpretation indicates that 2000 rpm provided the most favorable balance between temperature, oxidation rate, residence time, and exhaust flow. The results imply that exhaust modification should be evaluated at specific operating speeds rather than assumed to improve emissions uniformly.]]>
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