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Mercury Idle Adjustment?

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#1 Snowman


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Posted 23 December 2010 - 07:20 PM

I have a 90 HP Mercury (year 2000). The last couple of times out it has idled pretty rough and cut out a few times while at idle. Last 2 times out it was pretty chilly (and boat is stored in unheated garage) maybe the engine is a little tempermental but even when I let the engine run for a couple of minutes and then kicked it into forward gear the engine cut out.

So I removed the cowling and on the engine I see the "Idle Screw" but my manual does not say anything about adjusting the idle or what that "idle screw" is for. Can adjusting that screw help the engine idle a little better? Does anyone know how/what adjustments can be made? I do not even know is the screw should be turned clockwise or counter clockwise to improve the engine's idle performance.

Any thoughts or has anyone utilized this screw to adjust their own Mercury engine?


#2 TimW Texas

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Posted 24 December 2010 - 11:44 AM

Have you cleaned your plugs or changed them out . I leave the carb screws alone and try mine by the Idling arm it helps advance your timing on the side where the cables coming in. When you move the throttle cable does it idle better if so I only adjust those two. And try to synchronize them.

#3 Cracker Larry

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Posted 24 December 2010 - 01:40 PM

Adjusting the idle screw won't help it idle better. Like Tim said, rough idle is usually caused by dirty carbs, bad plugs, bad fuel or starving for fuel. Making it run faster won't fix it, it might hide it. I'd change the plugs and fuel filter first.
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#4 Curmudgeon



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Posted 24 December 2010 - 01:46 PM

If you motor idled well previously, but now it doesn't, adjusting timing and cables probably doesn't solve your problem. That screw has something to do with adjusting the idle, maybe speed, maybe mixture, usually in conjunction with other specific steps. You don't know how to do it (nor do I), so find someone who does ... :471_confused_face:

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