Fixed the semi-final problem, a bit of lean-stumble at idle. Richening didn't fix it...
When I went up to Top-End Performance in N. Hollywood to get the replacement power valve (mine's cracked, with a temp. fix) I mentioned this to the owner, Steve Nelson. He said sounds like idle jet too lean.
I pulled it out in the parking lot (simple screw plug outside the carb, above the fuel in the bowl and below the airfilter). Turns out to be a 60 installed; he said that's as lean as you'd ever use for a 258. 70 is normal.
Put the 70 in ($6), idle mixture now set correctly (3 turns in!) no more stumble. Well, I get a stumble every 10 - 30 seconds, but not bad for a parking lot fix.
This carb has no squirter on the secondary, so you gotta watch for bogging it at low speed (under 2000). But it's pretty damn good now.
I like Webers now. Wish I'd heard of 'em about 15 years ago. This one will do fine this year, I'll build Megasquirt TBI EFI this winter.