An apparatus and method of restricting flow of exhaust gas in an exhaust gas duct of a machine having an internal combustion engine is disclosed. The apparatus includes a closure member pivotably mounted relative to the exhaust gas duct within the exhaust gas duct interior. The closure member is pivotable between a first position wherein the exhaust gas duct is substantially unblocked by the closure member and a second position wherein the exhaust gas duct is substantially blocked by the closure member. An actuator is operatively connected to the closure member, moving the closure member between the first and second positions. A machine speed sensor and a throttle position sensor are provided, as is a manually operable switch. An electronic controller is connected to the machine speed sensor, the throttle position sensor, the manually operable switch, and the actuator, wherein the electronic controller operates the actuator in response to a sensed value of the machine speed sensor, the throttle position sensor, and the state of the manually operable switch.