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The OS Engines MAX-B21 engine is for entry-level and sports users as it is easy to use and has excellent cost performance. Based on the O.S. SPEED series engine, it has a well-balanced combination of smooth speed and power delivery and can be used in on-road and off-road racing situations.
The outer head is based on MAX-21XR-B VER.3 and has been reduced in weight for better performance. The shape of the combustion chamber of the inner head has also been revised to improve combustion efficiency and response in the low-speed range. In addition, more stable idling avoids stalling and equals easy carburettor adjustment.
Displacement 3.49cc / 0.213 cu.in.
Bore 16.27mm / 0.641in.
Stroke 16.80mm / 0.661in.
Output 2.6ps / 2.56hp / 34,000r.p.m.
Practical RPM range 4,000-41,000 r.p.m.
Engine Weight 361g / 12.73oz.