Uly06 vibration as "ring gear"

[Enzo]

I hope to be clear with my English...
Please can anybody tell me why my Uly06 (2600km)"trembles and leaps" when I slow down below 2000 rpm? If I pull the cluth this "leaping" disappears and it moves on perfectly. I have alredy controlled by myself the primary transmission: when I push the chain strongly with a screwdriver, it has a free play of 11mm.
Thanks for your help
Enzo

 

[Petrus]

Just don't slow down below 2000 rpm without pulling the clutch or downshift.