This is a tough question to answer on paper. I know on Evinrudes there are two notches in the middle cover ring that the throttle lever must be centered in when the cam just starts to open the carb butterfly. It is slightly different for the Johnsons, perhaps someone can post the pictures from the manual.
The exact indicator will vary depending on your engine’s exact model…but in one way or another there will be a notch or dots on the cowling that you can use to set your throttle lever. When it is set there…adjust the follower so it just begins to move the carburetor linkage. Here are a couple of pictures.