High RPM Miss KZ440

I've got a box stock 1981 KZ440 LTD with only 12K miles on it. It just started exhibiting a new problem. Right at 7K rpm I starts to miss. I really haven't dug into the problem. I did just pull the spark plugs and they look great. The service history is unknown to me. My son and I have driven the bike about 700 or 800 miles without issues until this cropped up. I can't tell if it is spark break up related to coils or bad plugs wires. Also could be a lean condition do to a new issue in the carbs/fuel system. I have not checked the valve clearances and don't know if they have ever been adjusted.
I have pulled, cleaned and lightly lubed the ignition advance mechanism. Last items, the bike does seem to take a long time to warm up, I'd say a full four minutes before it will run off choke. For the first time I also got a backfire when I throttled up to pull into the garage today after a 5 mile ride. Thoughts for what you would go after first?

ajsfirehawk wrote: Also could be a lean condition do to a new issue in the carbs/fuel system.
Last items, the bike does seem to take a long time to warm up, I'd say a full four minutes before it will run off choke. For the first time I also got a backfire when I throttled up to pull into the garage today after a 5 mile ride.

Carbs are starting to plug up, time to clean.


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