possible cause for backfiring in single cylinder motor

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  • benchrascal


    Replies: 24
    Topics: 6
    #1281

    I’ve inherited a bunch of forty year old small Japanese outboards ,mostly Nissans ,they’re all single cylinder.Trying to get a couple to run today and after cleaning the carbs and checking for decent spark and compression the only result is something like a backfire .One has an early solid state ignition and the other is fitted with an after market Atom computer module.Tried everything I could think of but neither wants to run at all ,just the occasional snort when I pull them over.


    legendre


    Replies: 389
    Topics: 8
    #14417

    First we need to agree on what’s meant by a ‘backfire’. Are your motors making bang-bang out of the exhaust, or out of the intake? True backfires come out of the intake / air cleaner.

    Bangs from the exhaust are +usually+ the result of a rich, un-burned mixture igniting somewhere in the exhaust tract. On the other side, bangs from the intake are +usually+ the result of a too-lean mixture causing the motor to ‘spit back’ out of the carburetor & intake. And it’s generally normal for an older outboard to spit out of the intake a few times when it’s started up from dead cold.

    Many older motors – not just outboards – have fairly crude starting devices, and they can act-up a bit when cold. If you can narrow this down, people will have a better idea of what to suggest.


    legendre


    Replies: 389
    Topics: 8
    #14418

    Oh BTW, congrats on finding some older Japanese motors.. for the most part, those things are pretty uncommon. 😉


    benchrascal


    Replies: 24
    Topics: 6
    #14452

    It is bang out the exhaust ,and then something like hydraulicing making it difficult to crank .Lots of resistance in motors that don’t seem to have much of anything wrong with them .I’m going to try to lean the starting mix right down to see if they are trying to gulp too much gas .Very frustrating because up until this point I’ve had very good luck with these motors.

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