With the development of high compression ratio or large-size engine, the cranking torque is getting higher, which causes the durability problem of starting system. Specifically, the starting motor and the one-way clutch are the most frequently wore parts. This kind of durability problem is also occurred in Stop and Go system, due to its frequently restarting process. Therefore, it is possible by using decompression device to reduce the cranking torque and to enhance the endurance capacity of the starting system. Furthermore, by reducing the cranking torque, engineers can miniaturize the starting motor and choose smaller capacity battery, and it also makes easier for kick start.A 150cc scooter was chosen as the example. The design, analysis and measurement with centrifugal type decompression device (CTDD) were discussed in this study. The systematic design procedures and tools were also provided to develop the product quickly. Finally, this study developed a decompression device in which the cranking torque was successfully reduced 42% and the cranking noise was also highly suppressed.