Be careful when adjusting this bolt. Loosen the lock nut and only turn the bolt in 1/4 turn in at a time. Tighten the lock nut back up, give the engine gas and let off the throttle, the point where the engine doesn't stumble when it returns to idle speed is where you leave the bolt. Turning it too far in will cause the stumble. Of course, depending on mileage, you may just want to get a whole new bolt. The spring inside them wears down over time.

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Regards,
Aaron