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  1. #1

    Default 1981 Johnson 15hp won't start, only backfires

    I can't seem to figure out the problem on this 1981 Johnson 15hp. I went through the carb so I know its getting gas. When I test for spark it has good spark. When I looked at a service manual it said to make sure the terminal wires were correct, no terminal junction on this motor. The timming seems to be off or at least it has the symptoms, I have gotten it to loudly backfire about 3 times now, timing? It has good compression and the flywheel is not slipping. What do you think? thank you in advance for any input.

  2. #2
    Join Date
    Apr 2006
    Location
    , Langkawi, Malaysia
    Posts
    5,750

    Default Re: 1981 Johnson 15hp won't start, only backfires

    Swapped plug leads or power-pack to coil leads? Broken flywheel key?

  3. #3
    Join Date
    Sep 2012
    Location
    N Wisconsin
    Posts
    123

    Default Re: 1981 Johnson 15hp won't start, only backfires

    I'm not sure about yours, but I had a similar problem with 4.5 I finally realized the plug wires were switched. Must have happened the previous fall when I winterized the motor

  4. #4

    Default Re: 1981 Johnson 15hp won't start, only backfires

    I'll go with the swapped leads as well.

    An easy check is to just swap the plug boots on the motor and try to fire it up again. If it runs well, then put the boots back on the other plugs and swap out the power pack to coil leads and your back in business.

    Backfires are usually combustion happening in the exhaust cavity, so since the exhaust is closed when your piston is at top dead center, I will assume it is firing when you are at bottom dead center.

  5. #5

    Default Re: 1981 Johnson 15hp won't start, only backfires

    I reversed the plug wires to the coils and it fired right up and purred like a cat, don't know why I didn't try that before, I guess I just didn't think any one would have monkied with the wires, the wires looked like they hadn't been moved since it was new. thank guys

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