Abstract: An exhaust system for a motorcycle having an engine mounted on a front half of a body frame of the motorcycle includes a plurality of first exhaust pipes extending from exhaust ports of the engine, a collecting section at which the first exhaust pipes are collected, a second exhaust pipe including a substantially straight portion connected to a downstream side of the collecting section and disposed under a crankcase of the engine, an expansion chamber connected to a downstream side of the second exhaust pipe and located under a rear wheel suspension arranged behind the engine, an exhaust outlet disposed on a most downstream portion of the expansion chamber, and an exhaust throttle valve and an exhaust gas sensor disposed on the straight portion of the second exhaust pipe.

Abstract: A 4-cycle engine for a motorcycle has a secondary-air supplier for supplying secondary air to exhaust ducts. The engine includes a recess, which is depressed toward the engine, on a cylinder-head cover for holding a control valve of the secondary-air supplier. The recess and the control valve are positioned between two innermost cylinders of the array of the cylinders. Check valves, which are connected to downstream regions of the control valve, are each disposed between two outermost cylinders of the array of the cylinders.

Abstract: An exhaust system for a motorcycle having an engine mounted on a front half of a body frame of the motorcycle includes a plurality of first exhaust pipes extending from exhaust ports of the engine, a collecting section at which the first exhaust pipes are collected, a second exhaust pipe including a substantially straight portion connected to a downstream side of the collecting section and disposed under a crankcase of the engine, an expansion chamber connected to a downstream side of the second exhaust pipe and located under a rear wheel suspension arranged behind the engine, an exhaust outlet disposed on a most downstream portion of the expansion chamber, and an exhaust throttle valve and an exhaust gas sensor disposed on the straight portion of the second exhaust pipe.

Abstract: A 4-cycle engine for a motorcycle has a secondary-air supplier for supplying secondary air to exhaust ducts. The engine includes a recess, which is depressed toward the engine, on a cylinder-head cover for holding a control valve of the secondary-air supplier. The recess and the control valve are positioned between two innermost cylinders of the array of the cylinders. Check valves, which are connected to downstream regions of the control valve, are each disposed between two outermost cylinders of the array of the cylinders.

Abstract: Separation of, or damage to, the inlet duct and outlet duct connected to a belt-type variable transmission is reduced, and durability of the belt-type variable transmission is improved, by preventing induction of foreign matter such as water, mud, sand or dust into the inlet duct. An induction box is provided between a front cover and a front upper part of a vehicle frame that extends above the front wheel axle shaft, and this induction box is fixed to a side of the vehicle frame. A cooling air induction port is provided in an upper face of the induction box adjacent to the bottom face of the front cover. A duct linkage port in the bottom face of the induction box and an air induction port of the belt-type variable transmission are connected by an inlet duct.

Abstract: Separation of, or damage to, the inlet duct and outlet duct connected to a belt-type variable transmission is reduced, and durability of the belt-type variable transmission is improved, by preventing induction of foreign matter such as water, mud, sand or dust into the inlet duct. An induction box is provided between a front cover and a front upper part of a vehicle frame that extends above the front wheel axle shaft, and this induction box is fixed to a side of the vehicle frame. A cooling air induction port is provided in an upper face of the induction box adjacent to the bottom face of the front cover. A duct linkage port in the bottom face of the induction box and an air induction port of the belt-type variable transmission are connected by an inlet duct.