The first thing to check is vehicle alignment. Has the motorcycle ever been in an accident? A slightly bent fork tube or axle will offset the vehicle alignment.
If you ride on a flat smooth even road surface do you feel the motorcycle want to pull to one side?
If your motorcycle has two rear shocks, check if the preload is set at the same level
I have a Kawasaki Vulcan 900. What are the possible causes for excessive front tire wear on only the left side? The tire is cupping but only on the left side