Engine exhaust assembly for a motorcycle

An engine exhaust assembly, comprising:

• a partitioning member provided in a pipe of a silencer arranged in the engine exhaust assembly for dividing the pipe into at least two exhaust passageways;
• a valve mechanism for causing variation in a surface area of one of the exhaust passages;
• a drive device for driving the valve mechanism to vary the surface area of said one of the exhaust passages;
• a connecting member for operably joining the valve mechanism to the drive device;
• wherein the drive device includes
• a pulley, said connecting member being wound around the pulley,
• a motor for driving the pulley, and
• a controller for controlling the motor, wherein the valve mechanism is controlled to vary the surface area of said one of the exhaust passages;
• a diaphragm located between said drive device and the connecting member;
• wherein said drive device is connected to a throttle valve chamber of a carburetor through a bypass controller and a check valve;
• and the drive device drives the diaphragm by applying negative pressure from the throttle valve chamber thereto, said bypass controller controls the amount of negative pressure applied from the throttle valve chamber, and said check valve sets the amount of negative pressure to be applied from the throttle valve chamber within a predetermined range.