Need help - trouble with KZ650 carburetors!

Here is the story ...

Last year my bike (a 1977 KZ650B1) ran flawlessly. Started first kick, idled great, drove strong. over the winter the caburetor bank decided to spring a leak at the middle fuel tube (the "T" shaped piece between the two banks of carburetors).

So I pulled them, split the carb rack and replaced all four O-rings for about $5. They don't leak. BUT - now it won't idle smoothly once warm and low-speed drive (i.e. when you let out the clutch) gets worse and worse the longer you ride. I've balanced the carbs, cleaned jets, floats, needle and seat, etc. and each time the symptom returns. It takes multiple kicks to start it as well. Plug color is a nice golden tan/gray after a ride or two, not dirty or black.

The bike is stock, 26,000 miles, running pod filters with the stock 4-2 exhaust. Have 15 pilots, 105 mains, air screws roughly 1 1/4 to 1 1/8 turns out from seated. It ran like this no sweat last year, now it's all headaches if i get mired in traffic and the bike has to idle a lot.

Oh, the charging system: good. Battery: good. Ideas?

Do check the valve clearances.
Some have said if the clearances are off, symptoms will often look like carb problems.

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