I received my New Set of Throttle cables for my 89 the other day, and they are Installed, Working Great.
---- Of Note: At the Carb, end, the New ones Have Vinal Inserts, I guess Yamaha took note of the Fraying at the #1 Carb hook up point.
---- Wether this will stop the Fraying problem, I don't know, but its worth takeing note of if you need to replace your throttle cables.