[Bluenoser86]

My 1987 (3 cylinder) 90HP Mercury runs really rough at idle and smokes badly. It smooths out at 2000 rpm under load and is generally a good engine. I am trying to teach my grandkids to water ski but the initial boat acceleration is initially poor.

I tried to adjust the carbs as per the manual but it runs so rough that it is tough to tell when the adjustment has any impact. I set the three carb adjustments at the generic 1 1/2 turns anticlockwise. The plugs seem equally as oily when the engine has been running at idle.

What else can I check or change?

[gregpro50]

Sounds like it is running rich and that the carbs need to be overhauled. It could be a float sticking or something like that.

[NathanY]

If what greg said dont work, try switching to full synthetic oil, do a decarb of that motor with Merc Power Tune, and change your plugs.

[NathanY]

If what greg said dont work, try switching to full synthetic oil, do a decarb of that motor with Merc Power Tune, and change your plugs