Re: 50hp evinrude idle adjustment
idle speed stop screw on throttle linkage.
Watch the linkage on the side of the powerhead whild somebody operates the throttle control. You will see the cable operating a tall lever that pivots in the middle. In the upper half of that lever you will see a long screw with a knurled head. That is the idle stop screw. Do not confuse it with the spark advance screw which is elsewhere.
The proper way to adjust it is to disconnect the cable and operate the linkage lever by hand, holding it against the idle stop. Then adjust the screw for your desired idle speed.
Finally, re-attach the cable and check that it pulls the linkage up against the idle stop when you put it in neutral. If it doesn't, adjust the black nylon attaching nut till it does (without strain).
This all needs to be done with the boat in the water because it will idle at a different speed in the water than it does on land with muffs.