Here's the skinny from Honda:
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In regard to the plug fouling, a few questions we need to look at:
Is the bike in stock configuration? (4-into-4 Honda pipes? If they are, are they HM300 or HM341 pipes? Stock airbox? Stock air filter?)
Did you reassemble the carbs with an aftermarket carb kit or genuine Honda parts?
How does the bike behave?
Do you primarily do highway or stop-and-go riding?
Are you running the correct heat range sparkplugs?
All of this needs to be established before we get into jetting changes.