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  1. #1
    Chief Petty Officer dorelse's Avatar
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    Default Looking at a 1990 Mercury 100 HP Outboard.

    Guys - A search for topics only brought me more questions.I'm interested in a 1994 Larson 18ft Bowrider with a 1990 Mercury 100HP outboard on it. Not sure yet how or what happened to the '94 outboard that I would assume was originally on it.Is there anything particularly bad (or good) about this motor? My last 1990 outboard, which was a 1990 90HP Force, was a POS so I'd like to avoid those kinds of quality issues. Now I know that for 1990 Force and Merc's were not together yet, so there's hopefully no comparison.I read about Mercury only putting gas to 1/2 the cylinders (on 4 cyl motores) during these years at certain RPMs...would a 3 cyl 100HP have the same technology (and problems), or is this a pretty decent outboard by reputation?I'll of course be doing a compression check, pressure testing the Lower unit seals, etc.Thanks!!!

  2. #2
    Moderator achris's Avatar
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    Default Re: Looking at a 1990 Mercury 100 HP Outboard.

    would a 3 cyl 100HP have the same technology
    Who makes one?These engines are known as '2+2'. They run the bottom 2 cylinders so lean that they don't fire (below about 1800revs), but still provide engough fuel to lub the nessecary parts. They still make the engines, and yes, IMHO they are good engines, but like all engines are only really as good as the maintenance performed on them.Chris.........
    The world takes on a whole new perspective when viewed from 100' below...



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  3. #3
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    Default Re: Looking at a 1990 Mercury 100 HP Outboard.

    Those engines are good engines. I ran one commercially for about 4 years and had no problems at all with it. They run exactly as Chris said. The 3cyl engines run on all three all the time.Good Luck.Butch

  4. #4
    Chief Petty Officer dorelse's Avatar
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    Default Re: Looking at a 1990 Mercury 100 HP Outboard.

    Would anyone be able to tell me the correct compression for this motor?Going to look at it on Tuesday.
    My Boat:
    1978 Glastron Carlson CVZ-18
    Project Thread - http://forums.iboats.com/showthread.php?t=357939

    1986 Bayliner Capri 1600 - SOLD
    Project Thread - http://forums.iboats.com/showthread.php?t=338265

  5. #5
    Chief Petty Officer dorelse's Avatar
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    Default Re: Looking at a 1990 Mercury 100 HP Outboard.

    Guys - Does anyone know the correct compression for this engine? I'm looking at it tomorrow!Thanks!
    My Boat:
    1978 Glastron Carlson CVZ-18
    Project Thread - http://forums.iboats.com/showthread.php?t=357939

    1986 Bayliner Capri 1600 - SOLD
    Project Thread - http://forums.iboats.com/showthread.php?t=338265

  6. #6
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    Default Re: Looking at a 1990 Mercury 100 HP Outboard.

    The correct compression readings will be ones from a known accurate gage, and will not vary more than about 5 psi from each other. The actual value is not as critical a factor as the variance between cyliders.Any more than 5psi variance and I wouldn't touch it. And I'm sure you'll hear it from others on the forum, but a leakdown test is a much better determiner than compression readings. However, in the absence of a leakdown test, having good compression readings is at least something!BTW the 2-4 cyl stepping thing is a bit quirky, if you're going to use the boat for wakeboarding you won't like it. The 2-to-4 switch is usually made at about the same speed you'd like to board at. If you're just fishing with it, it wouldn't be as much of a factor.Be sure you run it, preferably on a boat so you can see how it idles in gear and runs out at speed. Running in the driveway on a flusher will tell you little about the motor, so be wary if that's all you can do to evaluate it. These 4's run quite fast out of the water too, due to the extra-lean condition in 2 cyls.Quite frankly, I'd prefer an Inline Six but that's just me!G'luck and let us know how it turns out.......ed

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