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  1. #1

    Default 1984 mercury 75hp 2 stroke shifting into gear stalls

    hello everyone i had just bought the stated motor on a boat and it ran fine on muffs untill i got it on the lake.

    i start it and runs in neutral fine, soon as i shift into gear most of the time it stalls out sometimes it dont. if i push in the choke on the key while accelerating slowly it will stay started but want to cut out soon as i get it past a certain point it will run with out the key choke being pushed in i can run full throttle 32-33mph. i can even slow down to a fast idle in gear and its fine, i can even accelerate back up to w.o.t no problem but if i go into a no wake speed it dies out.

    i tried shifting slowly and accelerating slowly it dies
    i tried shifting fast and it starts to pick up and then quickly dies out.

    im hoping someone out there can figure this one out, thanks for your time.

  2. #2
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    17,311

    Default Re: 1984 mercury 75hp 2 stroke shifting into gear stalls

    Try opening the idle mixture screws 1/2 turn OUT (CCW).

    Jeff

  3. #3

    Default Re: 1984 mercury 75hp 2 stroke shifting into gear stalls

    alright im gonna try and get out soon as possible and try it. should it be done in neutral or in gear?

  4. #4
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    17,311

    Default Re: 1984 mercury 75hp 2 stroke shifting into gear stalls

    In gear, tied to a dock (or on a trailer) is best when adjusting idle mixture screws. Find you best idle, then add another 1/2 turn out (CCW). In the age of ethanol fuel, this has cured many a stubborn motor.

    Jeff

  5. #5
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    17,311

    Default Re: 1984 mercury 75hp 2 stroke shifting into gear stalls

    Nice write up, but you left out something: The later, "Power Dome" Mercs have a nasty reputation for doing this, and it's caused by blowby. To wit:

    Exhaust gasses pollute the intake charge in the crankcase, which burns poorly and causes lousy idle and meager power at low rpm. Ironically, the motor will start right up (clean air) but then crap out as the exhaust gasses build up; and this happens even when compression readings are only a bit low. I have a triple that has 135 lbs. compression, yet it won't idle below 1,500 without stalling. The only way I can get it into gear is to start it in gear, and that's hard to do.

    Older Mercs--that had lower compression ratios--don't do this. I spoke to a Merc dealer who told me that, when his customer's Big Sixes started doing this stuff, Mercury advised him to slap a new powerhead on it. In other words, don't bother to try to fix it. The only solution is a bore job.

    Sorry, but that's how it goes.

    Jeff

  6. #6
    Join Date
    Jun 2022
    Location
    Saskatchewan Canada
    Posts
    14

    Default Re: 1984 mercury 75hp 2 stroke shifting into gear stalls

    looks like you opened up an old post, but that answers some questions I had with my 75 hp.

    Has anyone modified the intake, and added a pod out the cover of the engine to prevent exhaust gasses from polluting the air intake?

  7. #7

    Default Re: 1984 mercury 75hp 2 stroke shifting into gear stalls

    Quote Originally Posted by mike83 View Post
    hello everyone i had just bought the stated motor on a boat and it ran fine on muffs untill i got it on the lake.

    i start it and runs in neutral fine, soon as i shift into gear most of the time it stalls out sometimes it dont. if i push in the choke on the key while accelerating slowly it will stay started but want to cut out soon as i get it past a certain point it will run with out the key choke being pushed in i can run full throttle 32-33mph. i can even slow down to a fast idle in gear and its fine, i can even accelerate back up to w.o.t no problem but if i go into a no wake speed it dies out.

    i tried shifting slowly and accelerating slowly it dies
    i tried shifting fast and it starts to pick up and then quickly dies out.

    im hoping someone out there can figure this one out, thanks for your time.

    did you ever solve this?

  8. #8
    Join Date
    Jun 2022
    Location
    Saskatchewan Canada
    Posts
    14

    Default Re: 1984 mercury 75hp 2 stroke shifting into gear stalls

    This was an old post from August 2014.

    I have an 1986 Mercury Mariner that was acting the same.
    Seems to be running pretty good now.
    I had to adjust the air fuel mixture screws. I have turned them each about 1, 5/8 of a turn out from seated.
    Seems to idle pretty good at this setting on mine. Boat trolls at about 2.6 MPH on a Starcraft SS160.
    Have to be sure that the motor is trimmed & running close to level. Had the motor trimmed up too high after launching and was stalling out until I got it trimmed down. Maybe hadn't fully warmed up either.

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