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1985 70hp Johnson stalls at acceleration

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  • 1985 70hp Johnson stalls at acceleration

    This motor stalls when I acccelerate from idie.The engine runs fine at top speed. Sometimes it will perform great and then the next time I accelerate from idle it will cough and kill. If I push choke when accelerating I can get it through the bad spot and it will run. So far I have put in new caburator kits, completly overhauled powerhead (rings,bored,pistons,bearings,gaskets). I have had it in two shops and had pickup timing checked, top speed timing , had the VRO pump disconected and mix oil to fuel at 50:1. I have replaced the Air jets from no.28 to no.33 as suggested in a 1987 factory bulitin. I have fought this for one year and am getting very frusterated with my Johnson outboard.Thank you for any help I can get.P.S. also tried diff. fuel tank.


  • #2
    Re: 1985 70hp Johnson stalls at acceleration

    Symptoms point to fuel. When you did the carbs did you blow out all the hidden passages with high pressure air from an air compressor. Carbs can look fine and have all the new parts but still be packed with crud.

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    • #3
      Re: 1985 70hp Johnson stalls at acceleration

      When you rebuilt the carbs, did you adjust the floats in the bowls to there proper level?

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      • #4
        Re: 1985 70hp Johnson stalls at acceleration

        I think I did a good kob at cleaning the carbs with carb cleaner and compressed air and I did adjust floats to spec.

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        • #5
          Re: 1985 70hp Johnson stalls at acceleration

          Hmm, sounds like you really covered the bases. Still sounds like a fuel problem but just for grins, you might want to pull the cowling off at night when its dark and run it on the muffs. Look around the ignition coils and the plug wires for electrical spark / arc.. Maybe someone else can jump in here, but it seems to me there are 3 ranges of jets on the carbs.Once you hit WOT, does it run smooth or do you still have to push the key in?

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          • #6
            Re: 1985 70hp Johnson stalls at acceleration

            I have a 74 70hp Johnson. It had a similar problem and it ended up being 1 of 2 things (I fixed a bunch of stuff but this is the combo that correct the problem) orifice/jets - went from a 30 to a 33 in the top (like you did) and left the bottom a 61D. The second was new fuel lines and hose clamps from the carbs to the tank. This corrected two problems. Stall (sputter) at take-off and a flat spot between 70% and 100% throttle. Good luck

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            • #7
              Re: 1985 70hp Johnson stalls at acceleration

              Wow, all those guys worked on it and nobody replaced the fuel pump diaphram? Your symptoms are a classic sign of a bad diaphram. You CANNOT do visual on a marginal diaphram and tell if it is bad either. Does it do this if someone is pumping the bulb?

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              • #8
                Re: 1985 70hp Johnson stalls at acceleration

                Yes I tried pumping bulb, also installed new thermostate but have not got a temp. of motor as yet to see if am getting up to 125 operating degrees. Tonight I pulled off carbs again and went throughly through them with carb cleaner and compressed air. I found nothing but kits don't show till Wednesday then I will test run. I did take a fuel pressure and it fell within spec.s

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                • #9
                  Re: 1985 70hp Johnson stalls at acceleration

                  When I hit WOT it runs well without pusing choke button.

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                  • #10
                    Re: 1985 70hp Johnson stalls at acceleration

                    Went for a ride also added foot electric choke. After running in water and playing with choke I am convinced that I am not getting enough fuel at low throtle. I also am quite sure that my carbs are clean (including any passageways and small openings). I noticed some play where the throtle shaft passes through the carb body. I wonder how much is too much? Next time out I will take some either and spray at these locations to see if I have air leaking.

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                    • #11
                      Re: 1985 70hp Johnson stalls at acceleration

                      Did you check your pickup timing? If you are too retarted when you hit the throttle it will have the same symptoms.

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                      • #12
                        Re: 1985 70hp Johnson stalls at acceleration

                        Yes my pickup and wot timing are set to spec. also carbs have been synced.

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                        • #13
                          Re: 1985 70hp Johnson stalls at acceleration

                          Can this problem be caused by reduced compression as the engine ages. This is a common problem for a great many(if not all) 3 cylinder Johnsons and Rudes from the 70's to the late 80's. I had an 80 70hp that had the same problem. Never could get it fixed. I did take the engine apart and hone the cyl. and new rings. It increased the compression about 10-12 lbs and helped alot. Still not totally. It is also a problem on my 1969 115hp Johnson if I have the low speed idle jets too far in. If the low speed jets are too restricted the engine will not get enough fuel without choking it a little. I cured that by opening up the needles. The 3 cyls don't have needles, just fixed jets.Maybe it is just planned obselescense.

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