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  1. #1

    Default 1986 Mercury 25HP XD Will Not Run

    1986 Mercury 25HP XD


    Can only get it to momentarily hit one time when I first start to work on it, then nothing, not even with ether/spraying fuel in carb


    Plugs seem to be dry


    Compression Cold is 98 on both cylinders/no leaking
    Just replaced both crank seals and wear sleeve
    Has Spark - Just Replaced the Stator because I thought spark might be weak/really good spark now
    Trigger resistance seems normal at 780
    Replaced one coil
    Flywheel Key is intact
    Carb Rebuilt
    Replaced both exhaust manifold gaskets to fix water leak into lower cylinder
    New Fuel tank, Lines, Filter


    Any ideas?
    Thank you in advance


  2. #2
    Join Date
    May 2015
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    2,240

    Default Re: 1986 Mercury 25HP XD Will Not Run

    Get a different gauge and re test? What is.good.spark? Has the carb been rebuilt recently?
    Last edited by flyingscott; 08-01-2020 at 07:03 PM.

  3. #3
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    May 2015
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    Default Re: 1986 Mercury 25HP XD Will Not Run

    Get a different gauge and re test? Do you have spark? Has the carb been rebuilt recently?

  4. #4

    Default Re: 1986 Mercury 25HP XD Will Not Run

    Quote Originally Posted by flyingscott View Post
    Get a different gauge and re test? Do you have spark? Has the carb been rebuilt recently?
    I retested the compression a few days ago with a different guage, 98 each cylinder. Yes, have a great spark, recently replaced Stator. The carb has been rebuilt recently, i Sent it off to a rebuild service. I cannot get engine to hit on starter fluid or when I spray fuel in the carb.

  5. #5
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    May 2015
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    Default Re: 1986 Mercury 25HP XD Will Not Run

    Are the spark plug wires on the right plugs?

  6. #6

    Default Re: 1986 Mercury 25HP XD Will Not Run

    Quote Originally Posted by flyingscott View Post
    Are the spark plug wires on the right plugs?
    Yes, plug wires are on correctly. I think I have low crankcase pressure / no fuel to the cylinders, thats why I changed the crank seals and wear sleeves.

  7. #7
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    May 2015
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    Default Re: 1986 Mercury 25HP XD Will Not Run

    Pull the transfer port covers off to look at the rings. 98 psi is not good good compression. Did you put the correct base gasket on? If you put the wrong one on you will cover the pump pulse port. Are you sure they put the right gaskets in your carb? And was it assembled with the correct gaskets?

  8. #8

    Default Re: 1986 Mercury 25HP XD Will Not Run

    Quote Originally Posted by flyingscott View Post
    Pull the transfer port covers off to look at the rings. 98 psi is not good good compression. Did you put the correct base gasket on? If you put the wrong one on you will cover the pump pulse port. Are you sure they put the right gaskets in your carb? And was it assembled with the correct gaskets?
    I read 90-100 compression when cold was good. The base gasket is the same as before. I actually sent the carb back for a second rebuild when I wasn't getting fuel the first time. They told me to buypass the carb by spraying fuel directly into the carb to rule out any carb problems. Will not hit with fuel sprayed into carb or with starting fluid.

  9. #9
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    May 2015
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    Default Re: 1986 Mercury 25HP XD Will Not Run

    Well as long as you read that is good. Change the green wires around on the coils see if it starts.

  10. #10
    Join Date
    Sep 2003
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    Default Re: 1986 Mercury 25HP XD Will Not Run

    If the wires to the cil are reversed, it will backfire and fight you when you yank the cord.

    Here's something to look at: The reed cage assembly has a rubber seal that has been know to leak. If that's the case it won't run. Also, when you put the carb on, be sure the little hole in the gasket (that operates the fuel pump) is lined up correctly.


    Jeff

    PS:I had one of those with low compression (but higher than yours). It ran but weakly.

  11. #11

    Default Re: 1986 Mercury 25HP XD Will Not Run

    Quote Originally Posted by fastjeff View Post
    If the wires to the cil are reversed, it will backfire and fight you when you yank the cord.

    Here's something to look at: The reed cage assembly has a rubber seal that has been know to leak. If that's the case it won't run. Also, when you put the carb on, be sure the little hole in the gasket (that operates the fuel pump) is lined up correctly.

    Jeff

    PS:I had one of those with low compression (but higher than yours). It ran but weakly.

    Yep, just pulled the reed block and that rubber seal was in bad shape... thank you.

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