clutch plates are engaged by 2 wafer washers. yours are probably flattened and not letting the clutch engage the plates.
http://www.instructables.com/id/SACHS-MOPED-CLUTCH-REPAIR-AND-RE-INSTALLATION/
https://www.mopedarmy.com/forums/file.php/6/57654/1219108968_sachsclutchweb.jpg
sometimes I can just take it apart and bend them a LITTLE.
Sometimes you have to clean the plates or groove them.