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Thread: '86 Honda 350x. Weak spark.

  1. #1
    Join Date
    Oct 2018
    Location
    Michigan
    --
    4

    '86 Honda 350x. Weak spark.

    Thank you for this forum.

    My '86 350 x has been a real trial. Now it seems as though the spark is very weak. The bike ran great last week, very hard to start though. I do not want to just start replacing electrical parts at random hoping for the fix. Would welcome feedback and direction. Thnx.

  2. #2
    Join Date
    Jan 2010
    Location
    Sulphur Springs,Texas
    --
    799
    Reading from the 350x manual.
    Weak or No Spark
    (1) Faulty Spark Plug
    (2) Fouled Spark Plug
    (3) Faulty CDI unit
    (4) Broken or shorted Spark Plug wire.
    (5) Faulty alternator
    (6) Broken or shorted ignition coil.
    (7) Faulty pulse generator
    (8) Poorly connected, Broken or shorted wires.
    (9) Improper pulse generator coil air gap
    • 1985 Honda 250SX
    • 1985 Honda 350X
    • 1985 Honda 350X
    • 1986 Honda 250R



    I Love The 350x. Its So Bad

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  3. #3
    Join Date
    May 2009
    Location
    S.E. Michigan
    --
    1,123
    Unscrew the spark plug cap from the coil wire (yes it will unscrew), snip 1/2" of the wire off, screw plug cap back on.
    - Frank

    1984 200ES Big Red
    1985 350X (x2)
    1986 250SX
    1984 Auto-X
    1984 ATC70
    1985 ATC70

  4. #4
    Join Date
    Oct 2018
    Location
    Michigan
    --
    4
    Thank you I'll give it a try.

  5. #5
    Join Date
    Oct 2018
    Location
    Michigan
    --
    4
    Thank you. It seemed to help initially. Now however the spark is sometimes weak, sometimes strong and sometimes intermittent. The coil does seem to have continuity. Where do I check next? Making me crazy. I just want to get it running and have some fun! Thanks for your help.

  6. #6
    Join Date
    Oct 2018
    Location
    Michigan
    --
    4
    On this bike I can kick it 100 times, nothing. Then all of a sudden it fires and then runs GREAT. At this point I am assuming an intermittent electrical concern. (Valve timing checked, New carb, new plug, has fuel) I am thinking that if the compression was poor it would not run smoothly, or at all. Quite a quandary. Once I get it to fire runs like a new bike. Any thoughts? Thank you.

  7. #7
    Join Date
    Apr 2012
    Location
    MI, USA
    --
    2,689
    Do you have a multimeter? Sounds like you do but doesn't hurt to double check.

    Jumping into the service manual and assuming it's electrical (makes most sense anyway), here's some specs to check

    Pulse Generator - 297-363 ohms (red connector coming out of the engine, disconnect and measure between the two wires from the engine)
    Coil - Primary coil resistance (the two spade connectors on it) - 0.16-0.2 ohms, secondary resistance is 3690-4510ohms with the spark plug cap off and one of the spade connectors (added photo link below)
    https://i.gyazo.com/1149afe14857063f...c760925d27.png

    Exciter Coil - Black/red wire to ground, spec is based on brand, Denso (ND) is 20-150ohms and Mitsuba is 200-350ohms.

    Last thing that comes to mind is the CDI box which isn't too easy to test, best process is to swap it with a known good unit.

    Very unlikely, but also make sure you're wire harness is in good shape, the Black/White wire is the kill wire, if it shorts to ground it will prevent spark. You can disconnect the wire near the handle bars to remove the engine kill switch from the circuit but it's unlikely to be intermittent.

    To me it sounds like a bad connection or one of the coil based parts failing (coil, exciter coil, or pulse generator). I'd say make sure all of the bullet style connectors are a tight fit, the two pin connectors from the engine look pretty clean from corrosion, and the CDI box has like new brass in the connectors (it uses sealed connectors). Not to try to spin this into making money or anything, but if you need a pig tail to repair the harness, or a whole harness, that's what I do, just shoot me a pm with what you need and I can work things out with you.

    I dug into the alternator/pulse generator section of the Honda 350x service manual, and I don't see a spec for the air gap, from memory I don't think it is adjustable on this machine, it just a basic bolt on setup.

    Another thing you could do to see if you have a weak spark is to pull the spark plug out and lay it against the head and kick it over. Bright blue/white is normal, anything orange/red is too weak. There's a proper tool to do this and it basically measures how far the spark can go, even a blue spark can be weak, but for the most part it should still run on it. This would atleast validate weak vs no spark when it won't start.

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