shame on me, i thought it was out, but haven't played with one in years. correct way to adjust is to use a vacuum gauge and adjust for highest reading. nest best way is tune for highest idle rpm if you have a tach.
The reason is these carbs have the idle control system reversed. The needle controls the air not the fuel like the older carbs do. Reason for that is emmisions. The factory did not want anyone richening up the carb so they 'fixed' the amount of fuel. They also often had plastic limiters on the needles so they could not be turned very far either way from the factory setting range.
