A speed control system is for a vehicle having an engine including a carburetor with a throttle plate moveable between a minimum open position and a maximum open position. The speed control system includes a ground speed limiter mechanism operatively coupled with the throttle plate and configured to displace the plate toward the minimum position as ground speed of the vehicle approaches a predetermined maximum value. An engine speed limiter mechanism is operatively coupled with the throttle plate and is configured to displace the plate toward the minimum position as a speed of the engine approaches a predetermined maximum value. Preferably, a control linkage is connected with the throttle plate and is moveable between a first configuration, at which the throttle plate is disposed at the minimum position, and a second configuration at which the throttle plate is disposed at the maximum position, the two limiter mechanisms displacing the linkage.