So I pulled the CV of of my 1997 1200 to service the float boul and top slide. As I was putting it back together, this part was on the bench. I am sure it is an external bushing but don't know where it goes. I found it on one manual diagram but it's not clear to me what it is for.

 

That is part #35 in the exploded view pic. it fits into one of the 4 holes in the vacuum piston cover, and acts as a brace for part #39, throttle cable bracket.
Remove phillips screw from cable bracket and screw from vacuum piston cover and pull bracket out, drop the shim in, reinstall everything. Do NOT overtighten 4 screws that hold the vacuum piston cover down. Make sure the vacuum piston rubber seal "seats" in the carb's top groove. Make sure the throttle bracket sits square on the carb's side fitment.

 

Thank you!