I had to trim (file) a little off of the end of the flower nut on my 66 c.c. (the small diameter end that screws onto the shaft and goes through the hole in the clutch plate).
The flower nut was too long and it would not allow the clutch plate to fully seat against the clutch pads.
The flower nut would bottom out when it was threaded onto the shaft and the clutch plate would be a tad too far away from the clutch pads.(causing the clutch to slip when i would try to get the engine started).
By filing down the end of the flower nut, it allowed the flower nut to screw in further, which allowed the clutch plate to seat properly against the clutch pads.
starts like a champ now with no clutch slipping at all.