I have a 2004 Yamaha FZ6 with 21,000 miles. At around 15,000 miles I started to notice a vibration in the handlebars at certain speeds. My front tire was worn so I figured that was the issue. At around 17,000 miles I replaced both tires but the vibration remained. I have had it to the shop several times, they rebalanced the front tire and replaced the front fork seals but the vibration remains.
When I am riding up to about 45 MPH and over 55 MPH I can take my hands from the handlebars and everything remains stable. But if I am riding between 45 and 55 MPH and I take my hands from the handlebars they start to shake and there is about a 3-4 MPH area around 50 MPH where the shaking is very violent.
Any suggestions would be greatly appreciated.