I believe Merc specifies proper idle RPM is taken n set with the engine at temp and in the water.
Also your idle adj screw will be were the throttle linkage rests, the throttle cable connects to a lever/arm on the carb, that lever/arm rest on a hard stop when your in N, there is a screw there that you can turn in/out that will adjust were that lever/arm comes to stop at. Adjust the screw in to add to idle RPM and turn out to subtract from RPM, 1/4 turns at a time so not to over do it.
The air/fuel mixture needles/screws will be along the base of the carb, you will notice they have a spring that pushes on the head of the screw between the carb body and the screw head. These adjust your air/ fuel ratio, if you turn them in you reduce or lean the mixture if you adjust out you make the mixture richer or increase it. Standard tuneing procedures say to turn the needles all they way in, don't torque down, just gently turn in until they stop, then adjust them out one an a half full turns. Start n run the engine and make 1/4 turns on then until proper RPM is achieved.
I have found in my experience you will get one of two answers to the question of what the proper idle RPM is, one will be with the engine at temp in water in N, the other is with engine running at temp with it just shifted into F.. Meaning shift from N into F then bring you shifter back as far as u can without shifting back into N...so the boat is under loadand moving toward. They will be two very diff RPM values, I have always been told the proper way is to adjust it is under load and the three engines I have worked on have all been 850-900 RPM idle under load. I'm sure someone with more knowledge of your engine will correct me if I'm wrong , just looks to be the standard as far as I have seen
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