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89 100hp Mariner compression test

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  • 89 100hp Mariner compression test

    Going to do a compression check on an 89 100hp Mariner this AM. I understand those are the 2+2 motors and I was wondering if there is anything different about compression checking those as compared to a standard motor. I am not familiar with this system so I was just wondering.

  • #2
    No difference just pull the kill switch lanyard to kill the spark and do the test. The 2+2 system is in controlled by the carbs only the ignition still fires all 4 plugs.

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    • #3
      Thanks for the reply. What is the thought behind the 2+2 system, is it less fuel and more economical to run or something else?

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      • #4
        The lower 2 carburetors only allow a wee bit of fuel in at idle.----That is for cooling and lubrication.-------For those who often idle for some time it is a fuel saving idea.

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        • #5
          Sorry, I keep coming up with questions the more I learn. Is this a system that is still in use or was this kind of a fad thing for a few years and then replaced with something else? Was it dependable or a mechanics (and owners) nightmare? Thanks

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          • #6
            mechanics (and owners) nightmare!
            1989 Four Winns 170 Cobra 3.0

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            • #7
              That system was used for close to 15 yrs. It allows for a pretty good idle and saves fuel. I had the 125 version and it is still one of my favorite motors. They are finicky and a factory service manual is a must have. They were only nightmares for people who had no clue how to take care of them or mechanics who were unfamiliar with them.

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              • #8
                It is a very simple concept !!!---Just not well understood like many outboard concepts !

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                • #9
                  Where can you find a factory service manual?

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                  • #10
                    Originally posted by utfyrfytr View Post
                    Where can you find a factory service manual?
                    A dealer can help you with that.

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                    • #11
                      Sign up today
                      or call mercury parts and they will give you a product # when you give them a serial #.
                      https://www.mercurymarine.com/en/us/.../parts-catalog

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