1974 Evinruded 9.9 HP question

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  • July 12, 2021 at 7:19 am #242549
    Fred Hickman
    Participant

      My 9.9 idles smoothly until she reaches operating temperature. At that point, she dies at idle. (She will, however, run well when in gear holding the throttle handle slightly above idle, OR wide open). I have installed a new carb kit, fuel pump, water pump, re-set the points to 020. I do not see evidence of a head gasket or water cover gasket leak. At this point, I am stumped and do not know where I should be focusing my attention. I need one of our “wise owls” to steer me in the correct direction.

      July 12, 2021 at 9:49 am #242579
      frankr
      Participant

        US Member - 1 Year (includes $3 online payment fee)

        This really doesn’t fit the symptoms, but have you heard that that model was notorious for fouling spark plugs? We couldn’t keep some of them running one weekend, brand new right out of the box. Worth a try anyway, try new plugs. Wait for someone to tell the latest plug type, which escapes me at the moment.

        July 12, 2021 at 10:10 am #242582
        outbdnut2
        Participant

          US Member - 1 Year (includes $3 online payment fee)

          I worked on one for a neighbor that had the same symptoms. After going into the carb three times and checking a bunch of other stuff, I replaced the new Champion spark plugs with NGK spark plugs (just because I had some) and it magically ran perfect! Don’t ask me why, but others here said they had experienced this too. Since then, I’ve used only NGKs in OMC 9.9s and 15s.
          Dave

          • This reply was modified 2 years, 9 months ago by outbdnut2.
          July 12, 2021 at 10:25 am #242593
          Mumbles
          Participant

            I’ll vouch for NGK’s to!

            July 12, 2021 at 10:58 am #242600
            David Bartlett
            Participant

              US Member - 2 Years

              Good luck! I spent a month chasing issues on the same motor. Never again! I would rather change the water pump in a Mark 10!

              David Bartlett
              Pine Tree Boating Club Chapter

              "I don't fully understand everything I know!"

              July 12, 2021 at 12:26 pm #242624
              Mumbles
              Participant

                If fresh plugs don’t fix the problem, I’d go thru the electrical system end to end. Starting with the plug wires, remove the boots and refasten the spring terminals after snipping a 1/4″ off the wires to ensure continuity. Same at the coil end. Make sure the wires core is in contact with the pin in the coil. Your coils might have the factory sealed wires on them and an ohm reading should be taken of both the primary and secondary circuits in the coils. Are the coils cracked or showing signs of aging? A bad coil can work fine when it is cold but will start acting up as it warms up.

                These motors use the Lo-Tension magneto and both sets of points must be clean and gapped equally for the system to work properly. What about the condensers, P/N 581419? They go bad with age and should be replaced and they are another item which will start acting up as they get hot. If everything checks out and all of the connections are clean and tight, the driver coil under the flywheel could be going bad. And of course, it to is affected by heat.

                July 12, 2021 at 2:16 pm #242645
                fleetwin
                Participant

                  US Member - 2 Years

                  The symptoms you describe don’t really make sense, so I want to be sure I understand them….You are saying that the engine idles fine until it warms up, then it won’t idle? But, it runs fine if you raise the throttle up? OK, well have you tried leaning the idle mixture adjustment a bit? Perhaps it is adjusted rich so it would idle well when cold, but then it would be too rich once it warms up…How about the carb syncronization? The engine won’t idle very well if the throttle does not close completely at idle…But, this would probably be more evident when the engine was cold, not warmed up…Nonetheless, these early engines had some strange linkages that tied into the carb butterfly that could be holding it open at idle… Is the engine getting up to temperature? They won’t idle worth a darn if they don’t warm up…And yeah, try new plugs, just cuz they might be new, doesn’t mean they are any good…The latest recommendation for plugs are the chamion L82C plugs gapped at .030″. Don’t have any experience with the NGKs, but guys have reported success with them… These engines are known for fouling plugs frequently.
                  I guess I would move on to ignition troubleshooting after checking the basics…Perhaps the ignition is breaking down once heated up. I would get a couple of those inline neon testers and put one on each plug (be very careful not to short out the plug leads on the block/engine pan). Probably best to run the engine early in the morning or late at night to make it easier to monitor the neon testers while running….Start the engine with the testers cold while it runs OK, then see what happens once it warms up and misfires… You will have to dig into the ignition if you can verify an ignition issue…
                  Please know that these engines had several updates that were supposed to be performed in an effort to alleviate plug fouling and ignition issues, hard to know what has been done to your engine. Let us know what, if anything, the neon testers reveal…

                  • This reply was modified 2 years, 9 months ago by fleetwin. Reason: correction
                  July 13, 2021 at 1:39 am #242701
                  JOHN HOLBIK
                  Participant

                    We had several of the 9.9s of this vintage at our resort and we had plug fouling problems .We switched to if I remember correctly to Auto;ite AE901x plugs and it helped a lot but not 100 percent.In about 1976 my good friend Don who was the manager of the propeller and engineering division at OMC came up to Canada for his annual fishing trip he told me there was a problem with the head design and they would be coming out shortly with electronic ignition.The reason they went with the energy transfer ignition was to make more room under the flywheel for battery charging .We sold off the problem 9.9s and bought new ones when the change was made they were great engines till OMC cheapened them with the cable throttle control.in the tiller handle and in a few other areas the ones from the early eighties wetre the best.

                    July 13, 2021 at 7:35 am #242712
                    Fred Hickman
                    Participant

                      What is the NGK plug number?

                      July 13, 2021 at 10:23 am #242721
                      outbdnut2
                      Participant

                        US Member - 1 Year (includes $3 online payment fee)

                        NGK spark plug is number B7HS for your 1974 9.9 HP, or the resistor version is BR7HS. Both will work fine. The resistor version just eliminates some interference in onboard radios if that is a problem.

                        Note that the “7” in the number is NGK’s designation for heat range and, opposite of Champion, the higher the number, the lower the heat range.

                        The B7HS replaces Champion UL-81C that was specified for your motor.

                        Dave

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