'Looks clean' and 'clean' are two different things. Has the carb been soaked in a bucket of carb cleaner? There are lots of passages that need to be clear and they are not visible. The main jet needle is hollow and has 2 sets of holes in it. You should be able to put your mouth over the pointy end and lower set of holes and blow through it and out the upper set of holes by the threads. If not, something is clogged up.
Carbs don't 'wear out' other than where the throttle shaft goes, and that is easily repaired and isn't the problem here anyway.
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