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150 Black Max idle too high...how to adjust?

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  • 150 Black Max idle too high...how to adjust?

    As the title says I have a 1983 150hp Mercury Black max that runs awesome and idles good....just higher than the recommended rpm's. So my question is how do I adjust the idle to be lower? idle adjustment screw/s? it says no more than 750rpm while in gear and im quite a bit higher than that. any info would be great!


  • #2
    Re: 150 Black Max idle too high...how to adjust?

    The idle is set by adjusting the intial timing. 750 RPM in gear means in the water and under normal load. On the hose out of the water an idle of 850 is recommended. The intial timing adjustment is done using the single screw located just below and to the right of the large pivot bolt on the throttle arm. This is the only place you should ever attempt to adjust the idle. However, and there's always that however thing, being able to adjust the idle successfully depend on correct link and sync adjustment. If that's been messed with or wasn't done correctly you'll never get the idle where it needs to and have it remain smooth.

    90% of the time when an older engine doesn't idle at the right RPM its because someone has done the link and sync procedure incorrectly and one of the carbs isn't closing completely. I see this quite often.

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    • #3
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      Re: 150 Black Max idle too high...how to adjust?

      The idle pick up screw (just below the pivot) is set during link n sync. Normally it doesn't need to be messed with.

      Several things will affect your final idle.

      One is water, which puts a small amount of back pressure on the exhaust, so you need to adjust it in the lake.

      Another is throttle cable adjustment. Take the cable off for idle adjustment, then adjust the cable and put it back on.

      The idle adjustment screw is the one on the very bottom of the throttle arm assembly.

      If it doesn't seem to set up right, you should get the book and go through the formal linkage and timing adjustments. Then it'll probably work just like new.

      hope it helps

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