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  1. #1

    Question 1985 mercury 150 issues

    Hello all, I hope I have posted in the correct forum as I am new to this website. I have a 1985 mercury 150 serial: 0a138816 that I got a week ago with a known issue from the previous owner where it bogs down and sometimes dies if you donít let off the throttle. I started diagnosing fuel issues first but could not find anything wrong with the fuel system (even rebuilt the fuel pump because that was my one thought in my mind) I started testing ignition next and found out my motor is only running on one bank of cylinders (135). (246) are not firing. I have compression tested, have replaced plugs, switch packs, and have ohm tested trigger and stator and they are within specs according to my manual for the engine. I am at a complete loss and would greatly appreciate any help on what I need to check/replace as my local marine mechanic (azle, tx) cannot get my boat in for a few weeks. Thanks in advance!
    Last edited by Celler555; 01-19-2022 at 05:53 PM. Reason: More information

  2. #2
    Join Date
    Nov 2011
    Location
    tennessee
    Posts
    5,353

    Default Re: 1985 mercury 150 issues

    Only 3 things will cause this: 1) stator down on one side. 2) switchbox bad. 3) blk/yellow on pack not firing pinched/shorted to ground. You in luck as this is easy testing...1) swap red/blue wire on switchboxes, if problem moves stator bad. 2) swap boxes if problem moves box bad, only replace as a pair and use only OEM, Serria,ProMarine and lastly CDI. 3) Blk/yellow can be pinched between boxes as it splits from single wire in harness above them
    Pappys Sales and Service
    Owner and Factory Certified Technician
    Former racer KDBA (Kentucky Drag Boat Association)

  3. #3

    Default Re: 1985 mercury 150 issues

    Quote Originally Posted by faztbullet View Post
    Only 3 things will cause this: 1) stator down on one side. 2) switchbox bad. 3) blk/yellow on pack not firing pinched/shorted to ground. You in luck as this is easy testing...1) swap red/blue wire on switchboxes, if problem moves stator bad. 2) swap boxes if problem moves box bad, only replace as a pair and use only OEM, Serria,ProMarine and lastly CDI. 3) Blk/yellow can be pinched between boxes as it splits from single wire in harness above them

    Thank you so much. Ill use this info tomorrow in troubleshooting. Hopefully itís not a bad stator!

  4. #4
    Join Date
    Jun 2013
    Location
    Duluth Mn
    Posts
    4,798

    Default Re: 1985 mercury 150 issues

    Welcome. Test trigger IN ALL THROTTLE POSITIONS. Why? A wire may be loosing continuity at more advanced timing positions, hence the "bogging".

  5. #5

    Default Re: 1985 mercury 150 issues

    Quote Originally Posted by faztbullet View Post
    Only 3 things will cause this: 1) stator down on one side. 2) switchbox bad. 3) blk/yellow on pack not firing pinched/shorted to ground. You in luck as this is easy testing...1) swap red/blue wire on switchboxes, if problem moves stator bad. 2) swap boxes if problem moves box bad, only replace as a pair and use only OEM, Serria,ProMarine and lastly CDI. 3) Blk/yellow can be pinched between boxes as it splits from single wire in harness above them
    I switched those wires around you said to and the problem moved. So it is my stator. Is it possible to run an higher amp stator on these engines? I found one through CDI that is a 15 amp vs the 9 amp it calls for. Im running some big electronics on my boat and if possible I’d like to upgrade the stator to the 15 amp I found. Is this possible or will I burn up my rectifier/battery?

  6. #6
    Join Date
    Nov 2011
    Location
    tennessee
    Posts
    5,353

    Default Re: 1985 mercury 150 issues

    Should be just fine...
    Pappys Sales and Service
    Owner and Factory Certified Technician
    Former racer KDBA (Kentucky Drag Boat Association)

  7. #7

    Default Re: 1985 mercury 150 issues

    Quote Originally Posted by faztbullet View Post
    Should be just fine...
    much appreciated for the help!

  8. #8
    Join Date
    Jun 2013
    Location
    Duluth Mn
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    Default Re: 1985 mercury 150 issues

    Pappy, can the rectifier get hotter?
    Last edited by timguy; 01-21-2022 at 08:11 PM. Reason: Typo

  9. #9
    Join Date
    Nov 2011
    Location
    tennessee
    Posts
    5,353

    Default Re: 1985 mercury 150 issues

    Same 4 bridge rectifier is used on 9 and 16amp stators...
    Pappys Sales and Service
    Owner and Factory Certified Technician
    Former racer KDBA (Kentucky Drag Boat Association)

  10. #10
    Join Date
    Jun 2013
    Location
    Duluth Mn
    Posts
    4,798

    Default Re: 1985 mercury 150 issues

    Excellent, thanks.

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