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  1. #1

    Default 1999 Johnson 90 hp will not idle

    Hey guys, I have a 1999 90 hp johnson that will not idle. It will run all day idled up but as soon as you try to idle it down it dies. I have rebuilt the carbs, changed the plugs, changed the gas, changed the ignition and checked spark. Everything seems to be sparking as it should but it will not run on low idle or in neutral. Do you think its powerpacks? The motor is the optical ignition motor and i do not know much about it. Any help would be great. Thanks

  2. #2
    Petty Officer 1st Class lyncraft_mechanic's Avatar
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    Default Re: 1999 Johnson 90 hp will not idle

    have you checked your compression? any signs of water in the any of the cylinders, one sign would be a abnormally clean spark plug.

  3. #3

    Default Re: 1999 Johnson 90 hp will not idle

    I have checked compression in all four cylinders and they are 120 in all. I have checked for water and there is none present.

  4. #4
    Honorary Moderator Emeritus tashasdaddy's Avatar
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    Default Re: 1999 Johnson 90 hp will not idle

    will it idle on muffs? if so the idle speed needs to be adjusted and fine tuned with the motor in water and in gear. 650-800 rpms. you also could still have some crude in the low speed jets.
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  5. #5

    Default Re: 1999 Johnson 90 hp will not idle

    It will not idle in the water or on muffs. I have completely rebuilt the carbs. I toke them back apart and everything was still clean. I believe i am getting fire to all cylinders but am wondering if it is enough fire. It runs like its missing if at higher idling.

  6. #6
    Admiral
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    Default Re: 1999 Johnson 90 hp will not idle

    Do a spark jump test, get the gap tester from autozone, cost less than $12, set at 7/16th's inch. It should be a blue crack!

    If it checks ok maybe its the link/sinc or spark advance.
    If the spark advance is retarded it won't run until it starts to advance.

    when throttle is opened ( on mine anyway) the spark advances first, then the throttle starts to open.

  7. #7

    Default Re: 1999 Johnson 90 hp will not idle

    i have tried the spark tester and at 1/2" it is a blue spark. I will have to look at the spark advance. thanks. I had a mechanic say it might be a "optical sensor?"
    Not sure but everything helps. thanks

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