650 is one of the most dependable motorcycles you can find.
If you have not already done so, look in the little storage compartment on the left side below the seat (opposite from the battery compartment) you open it with your key, and see if the factory tool set is snapped in the bottom (impossible to see, its all black, have to feel for it).
If you have it get the spanner out, take the seat off, and you will probably want to set the monoshock preload towards its max setting ( i think 6 or 7).
If you dont have the owners manual you can download it for free from the yamaha website, and there is a section on setting the shock preload.
It comes default to 3 from the factory, which is good for a 180 lb rider - and most people never touch it.