In order to improve the fuel economy and CO2 emission for motorcycles, manufacturers have developed and commercialized motorcycles equipped with idle-stop (also known as stop-start) systems. Some test data have shown that such motorcycles may cause 55% more exhaust emissions over the test driving cycle when idle-stop function is on, and fail to meet the functionality expectations of reducing emissions from such motorcycles. Two market sold idle-stop motorcycle types were tested on chassis dynamometer to investigate their transient exhaust emissions over six different driving cycles with idle-stop function on and off separately. Further more, the feasibility of emissions improvement by adjusting ECU calibration was also evaluated. The results show that the cumulative value of increased exhaust emissions during restart phase after engine shut off was higher than the cumulative value of decreased exhaust emissions during engine shut off phase, and that is the main reason for the motorcycles with idle-stop function on could cause more exhaust emissions. Further improvement of emissions by adjusting ECU calibration appropriately is feasible, even a 175 percent of emissions reduction could be achieved for the idle-stop motorcycles.