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You are talking about the black cap looking thing on the side of the carb right?
I don't believe those are rebuildable. You should not have any difficulty finding a new one at most auto parts stores.
I adjust mine this way. On a cool morning before you crank the engine press the gas pedal to the floor one time. Now rotate the choke cap until the choke butterfly valve on the top of the carb is almost closed all of the way.