Misfire at cruise, popping/afterfire at 3000RPM

Pulled the carbs today so I could send the base plates to Harold Demes -- he's going to replace the throttle shaft bushings. I noticed that the intake bores on the outboards looked significantly richer than the center carb, and secondly, the front outboard was richer than the rear. Why would that be?

Didn't have time to pull the plugs, but I suspect they're all going to be rich as previously mentioned.

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