Hi, I have a MPL slipper in my 907IE.
Some questions....
when the clutch is pulled in , should the basket stop spinning? Mine still spins until I put it in gear.

I was getting some slip after about 1000km of use. new barnet plates.

I pulled it apart and cleaned the steel plates, a very light 400 sand and degrease, and lightly sanded the plates as some had a blackish coating over them. When new they have an oily coating, I think I cleaned it off, was some time ago...

Anyway all clean reasembled and no slip.

One other item was that the wavy steel plates was showing rubbing on the high spots and the back of one had a "blue' spot where it had been getting very hot.

MPL specify a clearance of 0.6 to 1.2mm from the baket to the drum.
Mine is closer to the 1.2 so maybe its not releasing enough when the clutch is pulled in at the lights. Do other slippers have this sort of clearance?

thanks , any thoughts would be of great help

I have a slipper in my Multi so I don't know how it works vs. yours. They all use different ramps and balls.

If the trans is in neutral, then the basket can spin.

The Thickness/height of the clutch stack is important and that may be your slipping issue.

Make sure to lbe the ramps and balls of the slipper mechanism.