Traced though the air/fuel/exhaust/ignition systems--everything looked OK except for some black particles in the carb bowl. Figured it was either the 10 yr old fuel line or the petc0ck rubber bits. Replace the fuel line.
Used the mighty-vac to pull a vacuum on the petc0ck and it wouldn't hold vacuum. Seems like it ought to or I'd have unmetered air going in to the carb after the venturi. Also a leak at low vacuum (WOT) would cause it to not open up all the way.
Replaced it with a manual one from Eagle Mike & it ran great.
In the one step forward/two steps back department, when I got off I-70, the bike quit--the float had stuck open and was dumping about 1 gpm of gas through the carb vent tube.
Did a PITA roadside carb bowl removal and wiggled the float & it ran fine to home. Best guess--prolly got some dirt in the carb bowl from the new fuel line or petc0cok or the on-bike disassembly of the carb to check it for cleanliness.
Thought I'd pass the vacuum petc0ck findings on--I've replaced a bunch of them for fuel leaks, never for a vacuum leak.
If I'm missing something on the "not holding vacuum" bit, please let me know so I can further my KLR education!