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Results 1 to 11 of 11
  1. #1

    Angry 1985 mercury 50hp 4 cylinder--cutting back at wot

    Plugs been replaced---coils been replaced-----fuel been renewed---filter bowl has been cleaned---once it warms up good it starts cutting in and out at wot---you can feel it do it --acting like its running on 3 cyclinders---burning gas like crazy----trying to narrow it down on what it could be---i know it could be trigger assy---stator assy---module assy---just need some pointers here thanks

  2. #2
    Join Date
    Sep 2010
    Location
    ontario
    Posts
    9,878

    Default Re: 85 mercury 50hp 4 cylinder--cutting back at wot

    Maybe just a hole in the fuel pump diaphragm.

  3. #3

    Angry Re: 85 mercury 50hp 4 cylinder--cutting back at wot

    if thats the case wouldnt it do it even at low rpms---i can feels it kicking in and out like fires coming and going but i will check the diaphrams----while the engine is cold it runs like a new one---for instance i took it to the inlet about 2 months ago after replacing all the coils---put it in the water very cold day had to go about 5 to ten miles to get to our fishing spot---ran fine all the way up there --thought i had it fixed than on the way back it started doing the same thing again

  4. #4
    Join Date
    Sep 2010
    Location
    ontario
    Posts
    9,878

    Default Re: 85 mercury 50hp 4 cylinder--cutting back at wot

    So you did all that other work and it did not fix it ---Spent money on parts that perhaps it did not need.-----------Checking the pump won't cost a penny.---------------While you are at it do a compression test and check that you have spark that will jump a gap of 7/16" at each plug.---------------Run the motor with the covers OFF and see what it does.-------------------Look into the carburetor bores with a strong flashlight at full throttle and see what you see there.

  5. #5

    Default Re: 85 mercury 50hp 4 cylinder--cutting back at wot

    just finished checking it out --compression around 120 all 4------spark real good never died out the whole time i was out there --running at wot----never cut back while i was testing it--had a spark tester on it the whole time--it must only do it under a load pushing the pontoon boat----the parts i got were free from a local dealer i deal with ---only thing he had in stock with the older models--he gave them all to me because he only works on the newer models ----besides ive bought many mercury items including motors from him----but thats all he has so what ever the problem now its out of my pocket--thats why trying to narrow it down --thanks for help so far

  6. #6
    Join Date
    Sep 2010
    Location
    ontario
    Posts
    9,878

    Default Re: 85 mercury 50hp 4 cylinder--cutting back at wot

    Plastic " boost venturis " are in place ??----I have seen those broken.------------Water pump replaced ??----------------Pick-up tube in a plastic fuel tank checked.

  7. #7

    Lightbulb Re: 85 mercury 50hp 4 cylinder--cutting back at wot

    water pump has been replaced less than 3 months ago---fuel tanks has been changed---same action with either 3-----the other were replaced 6 months ago right after i bought it--had a marine tech go through everything dealing with the fuel part----has been sitting up for about 2 months before first usauge after doing all this--everything was fine just started this all of a sudden---ive had larger older engine do this and ive had entire ignition system replaced it solved the problem on them but dont know which piece it was---it was used parts i had taken off other old units i had in the past--but i dont have a complete ignition for this engine i could try --without buying a used one---

  8. #8
    Join Date
    May 2007
    Location
    Ireland,the only country in the world you can go North to go South
    Posts
    1,424

    Default Re: 85 mercury 50hp 4 cylinder--cutting back at wot

    It sounds like something,a break in a wire somewhere, is opening when the motor heats up Check all your connections and wires and clean them,I would look at the stator first.Test it cold first and see if it's within spec,between blue and blue/white @ R x 1000 5.7-8.0.Between red and red/white @ R x 1 56-76. No continuity between either red or blue to ground. Then heat the stator with a hairdryer and test again.If there is a big difference and way outside those figures it says in the manual,"Stator must be replaced".At $360 I hope not.Check the trigger,brown and white black @ R x 100 7-10 and the same between white and violet.

  9. #9
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    12,697

    Default Re: 1985 mercury 50hp 4 cylinder--cutting back at wot

    Are you sure it's timed properly? Sounds to me like it's way too advanced>

    Jeff

  10. #10

    Default Re: 1985 mercury 50hp 4 cylinder--cutting back at wot

    If you want to verify ign as your problem with a timming light connect to each cyl on at a time while under load [boat in water under way] hold timing light depress look directly at strob if you see stedy that cyl ok go to next a blink or erratic ignition problem, basicaly your testing as if you have ocalascope very helpfull for those come and go ignition problems. let me know what you find. by the way you have a very well designed engine properly tuned will run like a watch dont give up.

  11. #11
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    12,697

    Default Re: 1985 mercury 50hp 4 cylinder--cutting back at wot

    Update: My triple did the same thing as yours, and its problem was two of those little black covers on the connections on hte spark box. Two of them, close together, were not on properly and cross shorted out at WOT. The motor started and ran normally otherwise.

    Jeff

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