OK got out there this late afternoon and just wrapped up.
Short story - its fixed, idles nicely at 600, maybe 650 rpm. The short link was set too long even after multiple attempts to set it.
-Removed FCS, cleaned it by soaking business end in solvent, repeated 2X, flushed solvent squirted oil on it & reinstalled. Verified it works, but no love, no change.
- Checked that each plug was firing, cap and rotor (they look new), wires seem fine, all electrical connections tight.
- I eventually noticed that holding my thumb over the idle port/adjuster did little as I tried to approach an idle speed. I had set the short link per instruction again just today, but apparently the throttles were not quite closed (maybe the bores are a bit worn from throttle plates digging into them?). For me, the soft/hard close approach didn't do it.
So, yeah, I was way lean at idle, hence stalling/sputtering. I simply adjusted the short link until my thumb told me the throttles were closed. I figured this would sync the throttles with the pump. And bingo, it suddenly idled nicely.
The FCS seems to work really well now, maybe cleaning helped or maybe I'm rationalizing the time I killed cleaning it.......
- My ancient dwell tach says idle is a pretty even 600, but I think it reads 50 rpm low (I compared to another some time back). Either way, I'd prefer 7 to 800 rpm. But I still need to set mixture (and CSS) and make sure all is right, so maybe I'll gain a 100 rpm at the end of it. The idle o-ring is fine also, plenty soft and not squished. Don't know if the idle tower has the update (basically a larger hole), not sure if that helps idle.
-I'll see what else I learn here and update.
Thanks for all the help.