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Hi and welcome to JustAnswer,Thank you for the question and your patience. Should you still need assistance for information purposes only...Initially, it would appear to be an (uneven) air/fuel delivery issue. Foremost propose check would be to visual inspect the old sparkplugs particularly for their the burn color. Results of this would be significant as it would help determine a lean or rich condition.
Additionally with the Honda center/upright, check if all the carb bowls have equal fuel by draining individually through their drain hose and compare amount inside of each. This would help determine if 1 or more cylinders may be having a fuel starvation at higher RPMs due to low fuel level in the bowl.