This is a Pre-broken in engine based on the O.S. R2103 with an SMJ original printed cylinder head.

The Kabuto R21 has advanced as “Model ’18” with a revised cylinder liner, crank shaft and steel main bearing.

At low to mid-range, torque performance has been improved.

DLC coating is used on the crank shaft, embedded tungsten-weight on crank shaft and potted-tuning has been performed.

There is no change to the fuel efficiency of the former model.  Collaboration with Yurugix.