Not familiar with your bike but generally: On the starter, have you taken the side cover off and inspected inside?? If you don't have a manual, sometimes you can look up online parts microfiches and kind of tell how things are suppposed to go together. Something is worn or wrong inside where your starter engages. But manual is really what you need or maybe go to local shop and see if they will let you look at their manual. On the cable, there is a right way to route a throttle cable and about 200 wrong ways to route them. As you know, it shouldn't do what you're experiencing. Very dangerous. See if there is a another way to route your cable so it doesn't do this (again, manual probably has diagram). If the cable is just flat wrong, you can probably still order a new cable for this application, either through dealer or one of the many vintage bike online shops. There is some adustment built into the cable, but I suspect you've already decided not enough to get rid of your problem.