Start with basics, Its most likely a fouled plug you dont want to go rushing into stripping the carb down just yet if its been running ok before with this setup
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Try a new plug, if that doesnt help, I had a blocked spark arrester with the standard can that made the engine so it would barely rev, After trying everything else I took out the sparky and it ran better then ever before. I now run a answer pipe on it. Look at the airfilter too, Unlikely to be the issue, but it sounds like its being choked.
85 Tri-Z "Rumble Bee"
85 250R "Red Rocket"
83 200X "Flat Tracker"