prop spinning fast

ok so yesterday winterizing the 1994 Johnson outboard, this is the first time this ever happened,so I'm running engine in a big barrel and notice a lot of water being turned over the sides of barrel and noticed the prop was spinning fast enough to cause the water to splash out of barrel,first time this ever happened and it was in neutral.so I pulled throttle all the way up until the button on the side of throttle popped out,than put it back in neutral by pressing in on the button on throttle, I noticed it stopped spinning. the little plastic wheels that are on the engine attatched to the cables have to be adjusted? if so I would that happen out of the blue and if that is not the problem can can I do.Question though I never replace cables to boat I'm the soul owner always took care and always sprayed engine head down with lube to prevent corrosion. thank you guys and god bless this great country and to all that love to help others.

Not that it matters in this case, but it's best to also include the hp of the engine.

(Centering Shift Cable)
(J. Reeves)

When all is as it should be, the proper method to adjust the shift cable is to disconnect the cable from the engine. Move the shift linkage on the engine to find the center of the play in neutral, and when found, leave it centered.

Now, grab the end of the shift cable sleeve, push and pull it to find the center of the play there, and center that play.

Adjust the trunion on the threaded portion of the shift cable so that the centered play of the cable lines up with the centered play of the engine's shift linkage. Install and lock the shift cable with the retaining clamp in that position. That's it.