This is the O.S. SPEED B2104 Combo Set equipped with TB03 (T-2100, EFRA 2155) silencer with 80mm manifold (MB-01-80).

Specifications:
Displacement:3.49cc / 0.213 cu.in.
Bore:16.27mm / 0.641 in.
Stroke:16.80mm / 0.661 in.
Output:2.68 ps / 2.64 hp / 34,000 r.p.m.
Practical rpm range: 4,000-42,000 r.p.m. weight:352g / 12.42 oz.
Standard accessories
Glow plug T-P3 ・Reducer φ6Ⅱ、φ6.5Ⅱ・ Exhaust seal ring
Dust cap set 12-30(φ3、φ16、φ18)

Features:

The new piston/liner is conventional 3-port type enabling more torque over the power range.
The new crankshaft has DLC coating as we always do for OS SPEED engines. The two tungsten counterweights are embedded in the crankshaft contributing consistent idling and quick rpm down according to throttle move.
The thrust plate with surface treatment embedded in the cover plate reduces friction against a connecting rod to extend its life.
The boost port and the exhaust port of the crankcase are redesigned for optimum air flow.
The carburetor is trustable 22E type, which we have been using for B2103 Type R.
The cooling head is conventional round-shape type with standard height.