Lane,
I've had exactly the same problem on idle circuit intermittently only on #2 cylinder on my 1914cc with dual weber 40's for months. After taking the carbs apart and cleaning them, rechecking the valves, putting in a new spark plug, checking the cap ,rotor, and wires I did a compression test yesterday and all cylinders checked out at 135 Lbs. I filled up with hi test yesterday at the same station that I had gotten it a while back and the car ran like crap again. I usually get regular locally but was taking the tub to the drag strip (V-Dub Drag Fest)
After driving 160 miles on route 80 this am I ran the car 4 times down the track and did pretty well. I raced my buddy's new Fiat Arbath 3 times and beat him out of the hole each time but once his turbo kicked in he left me. I beat a bug sedan which had a stinger exhaust but I don't know what engine it had.My best times were 10.917 in the1/8 and 17.392 in the 1/4, top speed 75.89 mph.
I had a very experienced VW engine builder listen to my engine and he was convinced it was a plugged idle jet.On the 160 mile trip home this PM the car stumbled at idle and oil temp went to 240-I was pushing it too hard. It's time to change gas stations and install an oil cooler after I reclean the carb.
Joel