The purpose of this paper is to propose a control method to reduce acceleration shock in motorcycles. Reducing the acceleration shock is very important in improving driveability of motorcycles. Motorcycles equipped with manual transmission have some backlashes in the transmission, with large backlash especially in dog clutch portions. We have figured out that one of the main causes of the acceleration shock is the collision of the dogs at high relative angular velocity during acceleration. Also, our data analysis has revealed that there is a correlation between a peak value of the longitudinal body acceleration and the relative angular velocity at the moment of the dog collision. A simulation was undertaken to verify this phenomenon, and its results have made it clear that we need to decrease the relative angular velocity at the moment of the dog collision so as to reduce the acceleration shock. Therefore, we have developed a control method that estimates a relative angle of the dogs and implements ignition timing retard control just before the dog collision to decrease relative angular velocity at the moment of the dog collision. This control method is characterized as being effective even when a throttle is opened slowly, in which case the conventional method is not so. As a result of a riding test, we have proved this control method can reduce the peak value of the longitudinal body acceleration using this control method, and received good evaluation from riders regarding acceleration shock.