That sounds like a better "gig". I made a change many years back when I left "Stationary Engineering" behind and got into Aviation. The main reason was with the loss of my "Local" Job meant having to work remote in the "Oil Patch" and be away for long periods. Despite being a big "reset" I'm sure glad I did that.

I wonder if my "air pump" set up is a bit to blame for the small mixture change - I didn't check the pressure but might not like pumping cold air as well as the internals and the seals are all rubber and plastic..

I think your probably right with the viscosity -

All in all it was a super easy adjustment that took seconds - and it biased the whole curve and ran great. My standard setting is the knob detent so in summer I just wind back to that. I remember running both glow and gas in the cold and had much more trouble than this. I use to bring thermos's of hot water to preheat glow units to get them to light off..