Even with a brand-new Keihin carb, ISO was hard to tune. Startup has always been prompt, but reluctant to take throttle before fully warmed up. A bit of surging at steady part-throttle opening was another symptom. Idle mixture screw needed to be 3.5 or more turns out and idle speed adjusted to 2000 RPM or there would be stumbles. All pointed to a vacuum leak, which did not manifest itself when spraying brake fluid in all the usual suspect places.
I had sort of resolved to keep it "Stock", but enough is ENOUGH! Set to work deleting the evap recapture system, taking care to keep everything intact in case of a need for reversal. Turns out there was a vacuum leak, in an inaccessible place. See pics.
Idle speed now steady at 1800, mixture screw only 1.5 turns out. Will report again after first full-cold start.
The parts removed, fasteners retained.
Cracked 20 year-old lines letting extra air into manifold port?
Cleaned-up and lightened, lines neatly routed to lower frame.