Koso High Performance Scooter Parts include a very well known clutch that also carry’s the Stage6 brand name MK II. These are the 107mm and 112mm clutches mainly used in Straight Up Performance clutch packages for every thing from a Honda Ruckus to an Aprilia SR 50 Kymco Super 9 CPI Aragon plus GY6 50 models. There has not been a matching clutch bell for the 150 clutch which the smaller MK II from Stage6 have matching bells for adjustment of spring tension with forward facing clutch springs which makes changing a snap. A GY6 150 Straight Up Performance Clutch Kit would come with a MRP or NCY clutch bell at this time. There are also a Polini Bell used in some kits.
With a spring tension guide and weights that can be added to the clutch arms for higher rpm ratio for an added bottom end torque will match a performance variator with higher gram weight for a higher top end speed with all the bottom end that can had.