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1976 85HP Johnson Spark

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  • 1976 85HP Johnson Spark


    I have a 1976 85HP Johnson on the stern of my Mako 17. I was just curious if anyone knew where the origin of the park comes from. While the engine is running, as it charges the battery, does the battery also provide the spark for the plugs or does the spark come from the motor itself.

    Any help anyone can give me would be very much appreciated.


    Greg[br]1976 17 Mako[br]Shark River, NJ

  • #2
    he simple explanation is:

    The magneto generates electric current in the primary coil.

    The secondary coil increases the voltage of that current. (Voltage is like pressure that is behind elecricity as it travels thorugh a wire. High voltage is like high pressure. Low voltage is like low pressure.)

    The spark plug sparks, igniting the fuel.

    The fuel burns.

    The gasses expand, driving the piston.

    Work is done.

    Generating Electricity in the Magneto

    There is a permanent magnet on the spinning flywheel. When it spins past the primary coil of wire, a current is generated which passes down the wire under pressure towards the secondary coil. The energy of motion is changed to electrical energy.

    Unfortunately, at this point, even though there are enough electrons traveling down the wire, they are not at high enough voltage1 to cause the spark plug to spark.

    The electrons from the magneto pass through the secondary coil. Fewer electrons come out of the secondary coil but they come out with more voltage (pressure). These electrons arrive at the spark plug just in time to ignite the fuel and air mixture. The voltage going into the secondary coil might be as low as 50 volts, coming out as high as 15,000 volts

    Simple right? Take care, Murray
    Murray Gaskins[br]Valdosta, Georgia[br]Mexico Beach, Florida[br]Do not tell fish stories where the people know you; but particularly,[br]don\'t tell them where they know the fish.


    • #3
      I think you will find that the Flywheel/stator assembly supplies juice to the V/R which charge the Batteries. It also supplies juice to the ignition system for the plugs.......via a power pac or two and coils.


      • #4
        Thanks you both for the responses. It is very much appreciated.
        Greg[br]1976 17 Mako[br]Shark River, NJ


        • #5
          That is the long version - Short version is yes it provides spark for the plugs AND also charges the battery if the battery is in the circuit. Once the motor is running, the battery can be removed from the circuit and as long as the positive battery terninal is not shorted to ground, the motor will continue to run provided the key remains on and it has gas. Turn it off and it will not "electric key" start again (since the battery is removed), however, you will be able to pull start the motor and once it is running, your back to the motor running until it's shut off or it runs out of gas.

          1973 22 CC Milford, CT USA[br]


          • #6

            Thank you very much for the simple and direct response. It is truly appreciated.

            Greg[br]1976 17 Mako[br]Shark River, NJ