RE: K&B .65 Sportster (yup, more from me)
Hmmm...ok...
I just went and dug mine out of the box. I have an early .65 Sportster as well. No bushing and the needle is on the carb. I however have an eccentric adj. screw for the brass low speed adj. disc.
If you don't have the eccentric though, what's to keep the disc in place but o ring friction? (similar to Perry carbs )
I'm just thinking that if the disc rotated a few degrees...it doesn't take much...it can effect the entire r.p.m. range, not just the idle.