What happens if you loosen the clamp on the gov arm to it's shaft, and move the arm to the point the carb is wide open, and while holding that there, turn the gov shaft as far as it can go in that same direction, and then tightn the clamp? Thatbtakes all the slackmout of the linkage, and not sure if you have tried setting it up that way or not . . . .
That rod would be the governor shaft which is what the gear and plunger ride on.