Right at the top of the engine you will find the carb immediatley to the right on the carb you will see a flat head screw this will adjust your idle , helps to have a second person on this.
the idle tensioner and or the distributor.
poor spark, poor fuel grade, fuel pressure, spark plugs, not getting enough air... one of the above
its controlled by the computer. sometimes if you have a vacume leak or something eles is wrong they wont idel right. so you may want to check for a vacume leak somewere first
1978 80 Mercury Outboard IDLE ADJUSTMENT
You adjust idle with idle timing
The idle is not adjustible. You may need to clean the throttle plate to improve the idle.
There is none. It is electronic. Try replacing the idle motor.
How high is your idle? idle should be 800rpm good oil pressure is obtained at this idle
== ==
Idle speed is set by the PCM and is not adjustable. A faulty idle indicates a more complex problem that should be diagnosed.
The idle speed is set at the factory and is NOT adjustable.