Plus it idled fine
Out is leaner, in is richer. It's an air bypass into the throat and no fuel actually passes through it. Hence, out = more air (leaner) in = less air (richer).Mikuni manual will tell you how to adjust the mixture:http://www.mikunioz.com/tuning_manuals.htm
no collar, just a round plastic ring at the bottom, does turning out enrich the mixture?
mine has a round plastic ring at the bottom of the needle that fits into the hole the needle seats into.
Wrong! Not for the BS-29. CCW (out) is richer. CW (in) is leaner. It's a gas screw, not an air screw in the BS-29. The Mikuni site you've linked him to does not cover the BS-29 on the AVL engine.