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  1. #1

    Default Spark problems on a Johnson 90 hp 1985 (Model: J90TLCOS)

    Hi I just bought an old boat whit a Johnson 90 hp 1985 (Model: J90TLCOS) outboard motor on it. The motor had not been run for a few years. After cleaning out the carb and replacing the water pump I tried to get it running. But it would not start. I did a compressor test and all the cylinders where fine. I am getting fuel. But a weird think is happening with the sparkplug.

    So here is my problem.

    If I have no sparkplug in the cylinder I get a spark but as soon as the sparkplug is screwed in there is no spark on that cylinder. For example I remove all the sparkplugs and I get sparks on all 4 ignition cols , then I screw in the spark plug for cylinder 1 and I only get sparks on ignition cols 2,3,and 4.

    Does any one have any idea what is going on?

    Best regards

    Steinn

  2. #2
    Join Date
    Jun 2010
    Location
    Milton, Fl
    Posts
    546

    Default Re: Spark problems on a Johnson 90 hp 1985 (Model: J90TLCOS)

    You need to clean all the engine grounds you can find on the motor. Remove them and clean the block and the wire terminals, make sure you you clean both sides. This problem can drive you nutsssssss..... if you miss any..

  3. #3
    Join Date
    Feb 2001
    Location
    Central West Florida
    Posts
    12,018

    Default Re: Spark problems on a Johnson 90 hp 1985 (Model: J90TLCOS)

    What you're encountering is a common occurrence. The engine must turn over at least 300 rpms in order for the stator to energize the powerpack (ignition). The spark test is always made with the spark plugs removed so as to obtain the highest rpm which is needed to assure that the stator, powerpack, etc is functioning properly.

    Now, with the spark plugs installed, obviously the rpms are drug down somewhat, and even when the engine is in tip top condition, if you took a spark test with the spark plugs installed, the spark would be rather erratic.... this one fires, that one fires, but not all fire in the normal sequence. This is normal in the starting setup.... one plug fires which increases the rpms immediately and the rest of the plugs fire accordingly.

    However, if the engine has a poor battery, a tip top but undercharged battery, a loose cable somewhere, or a tight but dirty cable connection at some point... battery terminal, powerhead ground, solenoid, whatever.... this results in a voltage drop which in turn results in a low cranking rpm which will produce no spark/ignition.

    So as "coueytwo" suggests, clean all cable and wire terminals and whatever component they attach to that pertain to the electric starter system. A slow cranking engine = no ignition.
    Our questions require answers. If you refuse to answer our questions, how can we answer yours?

  4. #4
    Join Date
    Jun 2010
    Location
    Milton, Fl
    Posts
    546

    Default Re: Spark problems on a Johnson 90 hp 1985 (Model: J90TLCOS)

    Joe is right I left the starter/battery part out, a charged battery, clean grounds, and a good starter and you should be all set. Learned this the hard way..

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