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1975 70hp Evinrude, wont stay running, please help!

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  • 1975 70hp Evinrude, wont stay running, please help!

    Recently bought a 17' Sea Star with a 1975 70hp evinrude motor on it. Refurbished the entire boat after being told the motor ran fine and i thought it did when i bought it and started it up. What the seller didnt mention was that it only ran for 30 minutes then cut out and wouldnt start back up. not really sure what the problem is seeing as how i bought the boat only to redo the interior and not work on the motor. (not my specialty) a friend told me it might me the starter solenoids, so i replaced all 3 of them and it still didnt fix the problem. any help and/or suggestions will be greatly
    appreciated!

  • #2
    Re: 1975 70hp Evinrude, wont stay running, please help!

    First off, you need to get yourself an OEM service manual for your motor, and learn a little bit about it including the terminology. You don't have 3 starter solenoids on the motor. You have 3 ignition coils, which I suspect is what you were referring to.

    Start with the basics; compression, fuel, spark. Compression needs to be reasonable reading (+100 PSI) but more importantly all cylinders need to be within 10% of each other. Check for spark jumping a 7/16" air gap with a good snap and a bright blue bolt. Check your fuel connections and fuel lines for any air leaks, make sure your fuel pump is pumping fuel to the carbs by disconnecting the lines to the carburetor and making sure that its moving fuel when you crank the engine.

    Now, is your problem that the motor ran for 30 min and then just won't start up again, or is it that it can consistently run for about 30 minutes before stopping, and then you can't restart? If you can get it to start again once the motor cools off, you are probably not looking at a fuel or compression problem. 30 min is longer than it would take to drain the fuel from the carb bowls, so your fuel pump should be working. You still want to do a compression test, as you can start and run that motor on two cylinders.

    If you can get it to consistently start, but it dies after a time period longer than 5 min and you can't restart for a while, I would suspect an ignition problem. As the motor warms up, metal expands and can cause electrical shorts in the motor that will cause it to immediately die. Once the motor cools down, metal contracts again and it will be able to start. Start your motor and wait until it dies, then test for spark. If its not sparking, you need to troubleshoot your ignition system.

    Rgds
    1988 Stingray 176 SVB with Mercruiser 3.0L (181 CID) - The Ghostrider
    1995 Seadoo SPX 657x Rotax

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    • #3
      Re: 1975 70hp Evinrude, wont stay running, please help!

      Other can be the temp switch, maybe your engine is overheating and then kills the ignition. You should check if the cooling system is working properly.
      There are three ways to do things:

      1.- The hard way
      2.- The easy way
      3.- The way you have to learn....

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      • #4
        Re: 1975 70hp Evinrude, wont stay running, please help!

        Originally posted by mekkamaz View Post
        Other can be the temp switch, maybe your engine is overheating and then kills the ignition. You should check if the cooling system is working properly.
        with old motors, remember that it might be overheating and tripping the switch, or the switch itself may be bad and the motor fine. more likely the latter. So when looking for a problem that is indicated by a device, check the device AND the problem. And then, never rely on cut-offs, oil/heat alarms, etc. on an old boat.
        A man of constant boat tinkering.

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        • #5
          Re: 1975 70hp Evinrude, wont stay running, please help!

          Originally posted by mekkamaz View Post
          Other can be the temp switch, maybe your engine is overheating and then kills the ignition. You should check if the cooling system is working properly.
          No such function.

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          • #6
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            Re: 1975 70hp Evinrude, wont stay running, please help!

            Originally posted by daselbee View Post
            No such function.
            Only buzzer function? I saw sometimes that they connect this to kill sw in order to shut off....only in case....
            There are three ways to do things:

            1.- The hard way
            2.- The easy way
            3.- The way you have to learn....

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