At a glance
What can fail
The nut holding the primary sheave in the clutch can loosen and fall off. If it does, the engine may stall and fail to restart. You might hear unusual engine noises if this occurs.
What the fix does
Yamaha will mail you instructions to visit a dealer, who will replace the primary sheave nut and washer.
Summarized — see the official notice for exact wording, dates, and contacts.