Abstract: An assembly for selectively locking the angular position of a biased throttle grip mounted on an end of a handlebar to control engine speed is provided. The assembly includes a first member having a first face and adapted to be mounted on the end of the handlebar and a second member having a second face in close-spaced opposition to the first face and a third face spaced from the second face and in close-spaced opposition to an end face of the throttle grip when the first member is mounted on the end of the handlebar. The second member is mounted for rotation about an axis and for controlled shifting movement along the axis relative to the first member between a first position which corresponds to the unlocked mode of the assembly and a second position which corresponds to a locked mode of the assembly.