FlyboyDave, have seen the barrel guide screw back out on both my Saito 72s.
Have fixed this by gooping the threads with blue Loctite, and this seems to work.

I've noticed there is still some minimal barrel end-play in the carb body.
It is definititely enough to impact the low speed performance if I touch it.
I've noticed some variation in flight at low speed upright/inverted.
Both engines are mounted sideways on profile planes.
(i.e. Barrel pushing outwards upright, inwards inverted)

Has anyone seen a need for a stiffer carb barrel spring?
Idea would be to keep the barrel under tension in the body so it doesn't move around.