When you use this Polini 47mm Big Bore Kit in conjunction with your stock crankshaft you will increase your total displacement to 70cc! The manufacturer claims 9.7bhp at 10,800RPM is possible with this kit.
Fits Yamaha Zuma CW50 "Pre-Bug" Vertical Engines from 1989-2001.
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*You may need to modify your engine case to accommodate the larger cylinder.