Found a generator at the town dump with a 10hp briggs 19g412 engine.
Cleaned out its carb, ran well on half choke, surged otherwise. Could have dug deeper into cleaning the emulsion tubes but for $15 I just got this replacement carby
It now runs well on no choke, but starts hard. Needs a whiff of ether to get going. My "perfectly good" 3-month old gas has a summer RVP, may be an issue, am pursuing fresh fuel. But it runs in all my other OPE. Notably this thing's choke plate only closes to 45 degrees and is full of holes.
Anyway this unit has a knurled, nearly head-less hard-to-turn screw (with an anti-vibration spring) that seems to be for the idle mix. My question is, is turning this out/ CCW something that enriches the mix or leans it out (with more air)? It came screwed all the way down.
And does it even matter? At rest, when starting, the governor has the throttle wide open, so the idle circuit contribution would be minimal. There are little holes in the vicinity of the throttle plate, which, when it's closed, sensibly lead to the area of this screw.
One would think this is google-able, but the best info I can find is, yeah, guy, mess with this until it runs well.