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90hp Johnson bogging down at wot...

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  • 90hp Johnson bogging down at wot...

    I have a 1987 Johnson 90hp. I have replaced the plugs. Wires. Rebuilt carbs. Looked around on this site for electrical info. The coils are correct. The compression is correctm cannot figure this ot for the life of me. I am thinking maybe it is a power pack issue

  • #2
    I'd be leaning more towards a electrical issue...Check out CDI Electronics web site for diagnostic help.


    • #3
      I really appreciate that lewis..Thanks..do you know if there is a way to bypass "limp mode" on this motor.


      • #4
        I don't belive you can bypass limp mode on that engine. Here is a link to a set of online manuals. Have a look through it



        • #5
          I really appreciate that...i do have the factory manual for this exact motor..my father (who also is involved in this project) is definitely someone i would consider a master mechanic..and he took it upon himself to read this manual to try and troubleshoot this problem..we have pages of notes and temp reading. Have taken the boat out over half a dozen times..mainly JUST to test. But at this point im definitely thinking that certified marine mechanics must have certain secrets lol he had asked me if the oil temp engine temp sesors are normally open or normally closed..we have the colored (blown up) wiring diagram..it shows that all three sensors are grounded. I only ask because im reading that the "2 tan wires" coming off of the oil temp sensor..may be cut..to bypass "limp mode" because the VRO unit was removed on this engine..we run from a gas tank of a 50:1 mix. ANYONE with ANY other thoughts...please. It would be greatly appreciated


          • #6
            The 1987 model has no limp mode (SLOW), it didn't come out until later.

            All the tan wires are only for the horn and have no effect on the running of the motor other than make a noise.

            Try hand pumping the primer bulb when it starts bogging, this will help a failing fuel pump or a restriction on the fuel supply.


            • #7
              Lt fed.. Thank you. Yes i am basically going to replace the fuel pump. Since the vro is in fact removed..i was looking to get a decent one that will fit. I found one on wholesale marine . com..said "johnson 75 to 140 hp replacement fuel pump" its 85$ .do you think this is the one that would fit the 87
              with the vro removed. I beleive i have a 60 if that stands for anything worth taking into consideration.. I would go for the new fuel lines..but that was done already a time before we tested it for the 6th time on the water an before the new carbs were replaced and tested for the air pressure or whatever the, in depth, omc replacement install would consist of..was done by a trusted friend who works on boat engines when he has the time..bottom line. Is the fuel pump i mentioned a fit would tou say? Im having trouble finding it out here on the world wide web lol an im only 30..not good with computers..surprisingly. Any help appreciated


              • #8
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                Well.. Its been a while since my last post. Brome my ankle in Febuary and have been out of work for 7 months today actually. So the progress ive made with this engine (mostly my fathr, who is a very old school drag racing mechanic and very mechanically inclined an knowledgeable.. He is 69. and tuck in his ways basically refuing ti take to a boat mechanic..claims the engine is basicaly a simple concept.simplr than he had imagined..mostly due to the part there are NO computer parts on this engine (for the mot part at least) but anyway. I bought a new fuel pump..it is the oem replaceent for the pump needed when the VRO is removed. A sierra i beleive the name was. Long story short. We put it on. Toom it out for the 8th test run and a coil was bad haaaaa..just my luck. Becaue so far as mentioned ive replaced..both carburetor ( had installed by my fathers friend/boat mechanic) who presure tested them. Even gave me the litle depoits that were he recovered. Thought i was golden..then..th coil issue..which ws resolved, each at 120 124....dont quote those numbers but the old man was pleased lol. And all these were taken with the cowl off..running circles in the bay as he ran his tests. He even took the fuel pump hose off..fuel was flowing....not SPRAYING by any means. Not sure what the flow should look like but eemed ok to me..but what do i know. Also this was before we got the new fuel pump. Also new plugs amd wires..we are going to go out again. But if there is anyone who knows ANYTHING about this "wont get off its *** and start to run problem" im having...MUCH APPRECIATED