Try pulling off the muffler...
My 84 200ES was doing the same, i fought the carb for days, rebuilt it, put a new carb on and it got a little better but still fouling and wouldnt rev up smoothly. My muffler was shot and the packing moved around the muffler. I put on a new DG exhaust system and it was perfect, not running rich anymore, and not fouling plugs. So if the carb work doesn't help investigate the exhaust!
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1984 Honda ATC200ES "Big Red"
1982 ATC200E "Hondie"
1988 TRX300FW "Project Quad" Still in progress....