I ve had 2 Yamaha s (XS650,TRX850 both twins) and they were both excellent bikes.
Have you tried checking the fork oil ? I had a bike (the XS650) with the same sort of problem and one of the forks was nearly dry.

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07 865 Silver Bonnie....Bobbed Guards, Tacho, Grab Rail, Lucas Tail light, Mini Blinkers, Dart Screen, LSL Sport Bars, 1" Longer Hagons, 10mm Raised Forks, K&N Pods, Staintunes, 140/40 3 1/2 turns + 1 shim......etc....etc...
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