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1985 70hp Johnson - HELP !!

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  • 1985 70hp Johnson - HELP !!

    just got this boat/motor. it ran poor from the start. loads of water
    in fuel seperator and did the following.

    - dumped old gas
    - replaced all fuel lines, from tank thru to carbs
    - cleaned and rebuilt all carbs, including new high & low speed jets
    - new spark plugs ( gapped correctly )
    - new spark plug wires
    - rebuilt fuel pump
    - replaced one of 3 coils
    - installed tach
    - compression check ( all with 10 of 110 )
    - checked timing, ( is it really just stop screws )

    got boat to start well, idle well, run well up to 4000 rpms then it bogs down.
    squirt pre mix into top carb at wot and motor would jump up to 5500 rpms.
    same story with holding in primer solenoid. jumps to 5500 rpms.

    - cleaned all 3 carbs again. this time soaked in mineral spirits for 20 mins
    and worked them with a toothbrush. blew them clean with compressed air.

    put it back together, started motor with muffs in driveway, a little hard to start but ran okay at idled to 2000 rpm for a good 10mins

    took boat to water, backed it in, lowered motor in water. motor would
    not start. waited 15 mins. shot some starting fluid into carbs, motor
    started. ran on trailer in water for 10 mins, then pushed her off
    and headed out. got up to 5500 rpms for about 30 secs, then she died.

    got it started again, and limped in at 1500-2000 rpms. lots of coughing,
    gasps and choking the entire way. anything over 2000 rpms she'd die.

    my current thinking is, fuel problems are now solved but there is now
    a spark problem. i have ordered a new powerpack and will install it
    and test again this friday.

    my question: - am i grasping for straws with the new powerpack, does it
    really seem like there is a spark issue, what else should i look for, consider,
    do or test ?

  • #2
    Re: 1985 70hp Johnson - HELP !!

    Personaly I'd only opt for changing (expensive) ignition parts if I was sure it had no spark. But only after I ran the tests to make sure I was replacing the correct component.

    If holding the primer in and / or squirting fuel into the carbs cures the issue I'd say you still have a fuel delivery problem. I'd start by soaking the carbs in carb cleaner. You say you installed new kits, we'll assume the floats are set correctly and are free. We'll also assume you didn't forget the round gasket over the emulsion tube.

    You mentioned the water separator, have you checked it again for water / debris? Also make sure you have the correct Champion plugs.


    • #3
      Re: 1985 70hp Johnson - HELP !!

      don't wish to appear harsh here but as dhadley has mentioned, if you hold on the choke or squirt fuel into the Carby it runs OK (well sort of) so why do you come to the conclusion there is a spark issue? not saying there isn't but just think about it for a second!


      • #4
        Re: 1985 70hp Johnson - HELP !!

        seems like my post was not completely clear. there was a 2 step process.

        Step 1. Did everything listed, but soak and clean carbs with toothbrush.
        Results were, easy start, great idle, runs fine to 4000 rpm . wot bogs, squirt pre mix or hold primer solenoid jumps to 5500 rpm. obviously not the way
        she's supposed to run, so i keep trying.

        Step 2. Soaked and toothbrushed carbs, hit 5500 rpm WITHOUT squirt or primer push for 30 seconds. then died and ran worse then ever, poor idle,
        dies at anything above 2000 rpm, engine coughs, barfs, chokes, sputters.

        thinking is, fuel supply problem now solved but now have spark problem.


        • #5
          Re: 1985 70hp Johnson - HELP !!

          sounds like carbs still picking up trash any time you introduce external fuel to carb and it picks up it means that your not getting correct supply
          check your spark under load on trailer with timeing light
          when the prob occurs you will see the miss by looking into timeing light
          when you hit primer your motor should bog down not pick up sounds as if you have fuel prob run differnt tank and hose. bypass fuel filter if ya have one in line ,if that doesnt get it back off with the carbs pull welch plugs and jets
          soak overnight , blow with compressd air , i know you have had them down a couple of times but sounds like you have restriction in jetting.
          i pulled a carb five times with high speed bog finally took it to my boat guy
          i sonic cleaned it and used compressed air with small tip on it
          also had heavy float but that would cause over gassing on plugs what do your plugs look like
          Benny B


          • #6
            Re: 1985 70hp Johnson - HELP !!

            I'm not sure he tried squirting gas directly into it after it died after he cleaned the carbs, since he doesn't say he did.


            • #7
              Re: 1985 70hp Johnson - HELP !!

              correct, i did not try squirting gas into carbs after it died.
              seemed pointless as the motor was just barley running.
              anything over 1500 rpms and she'd die.

              this behavior was brand new. before the soak it would
              run fine to 4000rpms then bog at wot.

              after the soak it ran for 30 secs at 5500 rpms then died
              and would only do 1500

              when it was running at 4000 rpms squirting only made
              a difference in carb #1, that's why I opened them up
              again and did the soak, thinking fuel starvation in #1

              after the soak since it got to 5500 rmps without squirting
              or primer switch on, i figured carbs are clean fuel problem
              solved. then 30 secs later it died and i limped in


              • #8
                Re: 1985 70hp Johnson - HELP !!

                Well I got the new powerpack and put it in. Guess what same problems
                with a new twist. Now in addition to hard to start and running poor, I
                can't get it to idle at less then 2000rpms.

                So it seems my carbs or fuel supply are still bad. I got some berrymans
                and will soak overnight to see if that helps.

                The too fast idle has me stumped though. The butterflies on the carbs
                are closed and idle stop screw is not even touching the throttle arm/plate.

                Does anyone have some ideas to help me with the idle problem or/and
                thoughts about the carbs still not working right.

                Thanks, I eagerly await your replies....


                • #9
                  Re: 1985 70hp Johnson - HELP !!

                  After more research I'm thinking the too fast idle
                  is either a big air leak or the idle circuit in the
                  new power pack is not working right.

                  When I got the new pack, the connection
                  pattern in one of the rubber boots did
                  not match the old one. Attached is a pic.

                  I doubled checked I had the correct pack then
                  choose to swap the boots. I matched
                  up the wires correctly and got it to plug
                  in with no problems.

                  Does anyone have some ideas for how
                  to check the new power pack ?

                  Thanks !
                  Attached Files


                  • #10
                    Re: 1985 70hp Johnson - HELP !!

                    Update !

                    I fixed the fast idle problem, it was the power pack. One of
                    the pins was bent a little in the rubber boot and not making
                    a good connection. I also put three new spark plugs in
                    and gapped them all to .035

                    I got her running great with muffs, then took her to the
                    water. She started fine and I took off, ran at WOT 5600 rpms
                    for a minute or so.

                    Then she bogged down, started to cough, sputter back fire,
                    slog, choke, etc.... anything above 2500 rpms and she'd die.
                    I tried some pre mix in the carbs during this and it made no

                    Anyone have a opinion ?

                    It would be great to hear from someone with experience.
                    This is my first boat and first time I've worked on a
                    a motor since high school shop class 30 years ago.

                    Thanks !


                    • #11
                      Re: 1985 70hp Johnson - HELP !!

                      I am not a mechanic, but if spraying pre-mix in the carb did nothing I think you can rule out a fuel delivery problem. Sounds more like an electrical problem to me.
                      If I'm wrong I am sure someone will correct me, and even if I'm right I am sure they will give more insight into what to check out and/or fix. I'm about as new to this as you.


                      • #12
                        Re: 1985 70hp Johnson - HELP !!

                        HybridMX6 - Thanks for the reply, I've been wondering if anyone has
                        been reading my posts.

                        I'm at the same conclusion you are, electrical. I'm thinking coil
                        or rectifier or something else, just not sure which and how to

                        Does anyone agree or disagree or have a comment about how to test
                        or what else in the electrical area or elsewhere I should investigate.

                        Thanks !!


                        • #13
                          Re: 1985 70hp Johnson - HELP !!

                          Hello to you,
                          Is it overheating on you, maybe that is why it runs at 2,500 RPMs after it heats up. If not get a hair dryer and warm the coils up one at a time and see if heat is causing the coil to go out and thus losing spark on bad coil. Check your spark plug wires and make sure there good also no cracks, detoriation, dry rot etc. Also make sure your coil grounds are clean and shiney as well as all the gronds on the motor, nice and shiney clean. Hope this helps you out somewhat without having to buy pars and put them in to find out it is another part and waste money. Let me know, Bob


                          • #14
                            Re: 1985 70hp Johnson - HELP !!

                            Bubba - No idea if it's over heating or not. There is no temp gauge
                            so I have no idea about what the temp is. I don't even know where
                            the thermostat on the engine is. Can you tell me where that would
                            be located ? I'd like to inspect and see what it looks like.

                            The spark plug wires are all brand new, I will check for shiney grounds
                            plates on coils and the other grounds on the motor.


                            • #15
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                              Re: 1985 70hp Johnson - HELP !!

                              I haven't seen any mention of a spark check. Did you do one? What did it show?