I have an old1976 js400 jet Ski. the throttle and steering cable and steering plate are good beginning points. my steering plate is a little loose and needs to be tightened. My circling works OK. The throttle cable/steering cables and steering plate I lubricated, don't know if this helps. Kill switches can run up to 70 bucks on fleabay. A proper fitting one into start/stop switch box w/ good lanyard is cheap insurance compared to replacing an entire hull.
if you persistant on repairing circling, go to area where friend can meet ski at shore before ski crashes into shore. this will work as long as ski does not partially circle and the go straight. Several friends to catch ski would be best. I want my idle set JUST fast enough for ski to move and not die in water. A ski this speed may still get away from you, but shouldn't be overly fast.
The original Jet ski video, "A Jet Ski Story" on You Tube-- I believe is a good refence point for circling speed, slow and easy. Remember, the user is supposed to be fallen off, waiting for the ski to return like a faithful puppy. The speed slow helps user to swim and catch up w/ ski and remount easier too. My idle is still turned down a little too low and ski dies in water when off, a self kill switch. I still want to adjust idle for self circling. a ski going the minimum speed(1 to 3 MPH ) without dying at idle in water, can this cause serious damge to hull? It would be hard to believe so other than minor cosmetic.
just thinking of it, get some pool spagetti, or other large foam items to "bumper ski" to avoid hitting rocks or shore--directly in front of ski when tuning for self circling mode. I will do this for mine when adusting idle.
please posts updates what fixed your circling, this seems to be a common problem w/ older jet skis and could help a lot of people