Idling Problems...again

So its been a while since I last had issues with the CB360. I took it to a guy on my local forum who specializes in vintage bikes. He tweaked my clutch, adjusted valve clearances to spec, and synched my carbs for a low price. The bike ran perfectly for a few weeks. Now I am down to a single issue that has plagued me before:

Anytime that I ride the bike for an extended amount of time (longer than 25 minutes) I have issues with idling at stoplights. The revs will go down to the 1.3k range and stay there for a good 5-10 seconds. Then it will start to stumble, stutter and the bike will die. I can restart the bike right afterwards with no trouble, but to keep her going, I need to lightly apply throttle to 1.5-2k RPMs to stay "alive". I thought about just adjusting the idle screws to a higher RPM this is probably bad for the engine and plugs.

What could be the possible culprit? Compression is good (155 left, 160 right) carbs are rejetted and synched, spark plugs are slightly dark but otherwise good. Someday I am going to try out a new condenser that I had lying around, and I have a new battery and plugs coming in sometime in the mail. Thanks in advance!