A vehicle has a straddle seat, a handlebar, an engine, an electronic control unit (ECU), a throttle valve, a throttle valve actuator, and a throttle operator. A throttle operator position sensor senses a throttle operator position. A vehicle speed sensor senses a vehicle speed. The ECU sends a control signal to the throttle valve actuator based on the throttle operator position and the vehicle speed. The throttle valve actuator adjusts the opening of the throttle valve in response to the control signal. If the vehicle speed is lower than a predetermined maximum vehicle speed, the throttle valve actuator adjusts the opening of the throttle valve based on the throttle operator position signal. If the vehicle speed is higher than the predetermined maximum vehicle speed, the throttle valve actuator reduces the degree of opening of the throttle valve. A method of controlling an engine is also disclosed.