That would be a tough one to fix, thin as it is it couldn't be helicoiled. If you could take it apart and hold the lever on a flat surface and peen it to make the screw fit tight it would probably hold if you are careful about tightening the lock nut.
I have solved the problem. I took a 6mm bolt the same height and cut a slot in the top of it. With some help to lold the throttle open I drilled the hole and taped to the new size this works great. I had to use a spring out of a old valve body and cut it to the proper height. Was able to sync the carbs and off we went no problems at this time. Anyone know if the 83 has a bit of a roll to it at idle or is this maybe the idle mixture adjustment.