This is the OS B2103 Type R engine with OS T2100SC exhaust system.
The OS B2103 Type R engine is a 5-port long-stroke engine that offers great power at medium-high speeds. The crankcase, the crankcase cap and the carburetor feature a new design. The new DLC-coated crankshaft has two tungsten counterweights for smooth rotation and better balancing. It shares the same new features as the Type S engine except the cylinder and the cooling head which has a standard round shape.