Things that are consistant are usually mechanical. Things that are intermittant are usually electrical. So, with that said, here is what you might look at. If the bike goes "pop, pop --- pop, pop, pop --- pop", you most likely have a fuel problem. So, ride the bike and when it is "popping", slightly put some choke to the bike while holding the throttle in the popping area. If that straightens out the popping, you have a fuel problem. You will also notice a smoothing out of your low speed surging (some feel it is a "touchy throttle linkage"). You have a vacuum leak and or a low speed jet plugged. The vacuum leak that I would suspect is between the carbs and the engine (the rubber boots). Are they cracked? In otherwords, it is running lean. I have also seen bikes that act the same way when the owner turns the slow speed idle mixture screw out 3.5 or more turns.
If adding a little choke does nothing, then it is probably in you emission control system (if so equipped).

 

Set the mixture screws at about 2 to 2.5 out (depending on elevation where you live. Higher the elevation the less turns out). Also, if you are taking the carbs off, check those small low speed jets. They are real small (hard to see through at Classic's age!). Heck, I think I used a piece of 12 ga. stranded copper electrical wire (THHN) unwound it and used one strand to push through a piece of crud when my low speed jet was clogged. That is how small those holes are. My bike back popped and when I cleared that small piece of crud, it cleared right up and stopped the popping. Now after letting it sit unused for about 8 months, I have small pop again and need to use a little bit of choke to stop the popping. Looks like I will be joining you on a carb tear down, but I will put some "sea foam" (auto stores have it, it is a cleaner additive) in it, run it and see if I can get it to clear up.