While coming back from a trip to Tulsa this summer I noticed my speedometer would start acting like our old bikes with a cable when they were about to break. It would swing back and forth for a little bit and then settle down and work ok.
This continued only from time to time after I returned home.
I found the culprit when I recently changed the belt. The wire running to the speedo sensor had come loose where it was attached to the body and was rubbing the tire. It only had a couple of strands holding it together. I cut the bad section out and soldered the connection back together, covering it with heat shrink. I then tie wrapped it so it couldn't do this again.
Pryor to the trip I did change the rear tier so maybe I disturbed the wire then.
Just wanted to relay this info in case somebody else sees this problem.
Take care, Dick