First off replace both the needle and the needle jet. They both wear. Make sure you put the needle back in the correct notch if it's adjustable - may not be.
Second, I suspect that the carb is dirty, and needs a thorough cleaning, so I'd do that, then make sure the mixture screw is properly adjusted. This often causes the symptoms you describe. Probably lean, but then most bikes these days come a little lean from the factory. Richening the low speed settings often helps.
Also make sure the air cleaner is clean, and change the spark plug.
Check valves while you're at it - BEFORE you try to tune/adjust the carb - carb should be LAST after everything else is done.
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Grant Johnson
Seek, and ye shall find.
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One world, Two wheels.
www.HorizonsUnlimited.com