Rotate the head all the way counter-clockwise to completely close, then point with the arrow on top and the spray pattern will open up from that direction clockwise as you rotate the head clockwise....
Toro 640 series industiral sprinklers are difficult to adjust by virtue of the fact that the gears are specifically set at an assigned angle. This differs from other well-known irrigation companies...
How to Adjust Toro Super 600
To Increase Arc (A) Start with nozzle at left stop. (B) Press and hold adjustment button down. Rotate nozzle clockwise to desired amount of arc increase, then release...