S-Stage kits feature an upgraded aluminum cylinder for less weight and fit the XR50 only. Below are the specifications of the kit.

Bore: 52mm (39mm stock)
Stroke: 41.4mm (41.4mm stock)
Compression Ratio: 11.5 : 1 (10.0 : 1 stock)
Intake Valve: 19.0mm (19.0mm stock)
Exhaust Valve: 16.0mm (16.0mm stock)

More than double your XR50R power!
This is the kit that you have been waiting for. Your one stop, easy to bolt on 88cc XR50R kit. This is a complete kit made and tested specifically for the XR50R to boost the HP from 2.6 to 5.8 and double the torque to 9 ft. lbs.!

This is a complete kit that comes with the following:
· 88cc aluminum cyclinder with Skid Plate Mounting Tabs
· 88cc piston, rings, circlips and wrist pin
· Performance roller bearing camshaft
· Complete gasket kit
· Pre-jetted PC18 Keihin carburetor with throttle cable, mounting hardware and gaskets
· Aluminum high flow intake manifold
· Takegawa high flow air filter
· K&N crankcase vent filter
· Complete mounting instructions with pictures

This easy to install kit is ready to bolt on the day you get it!