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  1. #1

    Default Need Advice on 1991 Johnson 90HP

    My father recently gave me a 1990 Cajun with a 1991 Johnson 90Hp V4 on the back. I need some advice on repair or cutting my losses. I'm a fairly advanced shade tree mechanic so large\complex repair I can most things but I'm also not wanting to dump a ton of time\money.

    Some BackGround.
    1. Boat had been sitting for 2+ years.
    2. My father said the boat has always been hard to start & idol since he has had it for around 6 years.
    3. Once it was running said it always ran great once warmed up.

    Current
    1. It hates to idol and will really only crank with extra throttle applied
    2. Took it on the lake and after bogging\turning very low RPMS around the lake for 30 minutes it would slowing ramp up and run really good and fast. If I slowed down it would take another 2-3 minutes to get up to a decent speed again.
    4. Took it home and changed spark plugs and had nice solid looking spark on each wire.
    5. Drained all the gas and sprayed 2 cycle carb cleaner in the carbs
    6. Took it back on the lake and it would never plain back out and gain speed.
    7. Ran a compression test today and everything is between 60-72 pounds :-(.

    Just needing options if I should cut my losses or maybe try new head gaskets and carb rebuild kit. I got about 1k invested at this point between the batteries\title\and floor repair.

    Thanks
    Alton
    Last edited by alton987; 08-10-2020 at 05:27 PM.

  2. #2
    Join Date
    Sep 2010
    Posts
    20,307

    Default Re: Need Advice on 1991 Johnson 90HP

    No such thing as one of those in good condition being hard to start.-----It should show around 110 / 120 PSI-------So you have a bad gauge -----Poor testing technique ( battery / starter motor ) .----Or a motor that needs work.-----Might as well pull the cylinder head off and looky see.---Cylinder head is warped as they all are on 30 year old motors.-----Head gaskets are cheap !!

  3. #3

    Default Re: Need Advice on 1991 Johnson 90HP

    Updated with pics with heads opened up. I have very little experience with 2 cycle but I'm assuming this is not normal... :-( Click image for larger version. 

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  4. #4
    Join Date
    Sep 2010
    Posts
    20,307

    Default Re: Need Advice on 1991 Johnson 90HP

    There you have it.-----Typical broken piston rings.----Every one of these V-4 crossflow motors will suffer the same fate !!----Seen it countless times myself !!!----These are an easy fix for me.-----If you have to pay a marina you will be shocked at the cost for 4 new pistons to be installed.-----Can be done by a novice with patience and some simple tools !

  5. #5

    Default Re: Need Advice on 1991 Johnson 90HP

    Quote Originally Posted by racerone View Post
    There you have it.-----Typical broken piston rings.----Every one of these V-4 crossflow motors will suffer the same fate !!----Seen it countless times myself !!!----These are an easy fix for me.-----If you have to pay a marina you will be shocked at the cost for 4 new pistons to be installed.-----Can be done by a novice with patience and some simple tools !
    That is what I figured..Maybe if I was younger or had more free time. Off to Criaglist\Facebook Marketplace.

  6. #6
    Join Date
    Nov 2011
    Location
    tennessee
    Posts
    4,665

    Default Re: Need Advice on 1991 Johnson 90HP

    Dang aluminum termites......
    Pappys Sales and Service
    Owner and Factory Certified Technician
    Former racer KDBA (Kentucky Drag Boat Association)

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