Tell me about the diode board on an Airhead.

Discussion in 'Airheads' started by Hair, Apr 10, 2010.

  1. Hair

    Hair Outside the boxer

    Joined:
    Dec 18, 2003
    Oddometer:
    14,865
    Location:
    Northern New Mexico
    My R90 died on me today. It all started yesterday. Before that the bike never missed a beat. Yesterday I was riding it into Santa Fe. The bike would start cutting out intermittently. The cut outs were very short in duration. And seemed to be only happening when I was climbing a hill at high speeds. Today I had to ride it to Albuquerque. Again it was cutting out intermittently. The cutouts got longer and longer. They also started happening at lower RPMs. Then on the way home it died. I pulled the carb bowl covers. The gas looked good. I checked the points they looked good too. I've heard that the diode boards die on these things.
    #1
  2. beemer67

    beemer67 Really Old airhead

    Joined:
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    Fish Limb, B.C. Canada
    The diode board just changes AC current from the alternator into DC current to charge the battery. The fact that you keep starting the bike implies the charging system is not your problem.

    More likely to have a coil failing.
    You mentioned points but is the rest of the system still stock?

    I used to have an ACCEL igniton amplifier on my dual plug RS, still using points, and when this failed it caused sporadic engine cut-outs, but usually it started again after a cool down..
    Check the wiring to the coils, making sure no short circuits or broken wires that can be causing an intermittent problem.

    You also said the 'gas looked good', what ever that means. How is the level in the float bowl? Is going up a hill cutting off the flow? Long shot.

    Check things dirty points, run a business card through a few times. Make sure your kill switch isn't flaky
    #2
  3. bmwloco

    bmwloco Long timer

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  4. Hair

    Hair Outside the boxer

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    Location:
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    I will check the points again and the coils. I am an old farm boy. I have looked at many a points in my day. They looked new and they are opening about the right distance. Once I get the bike home I can run through everything.

    Thanks for the link to your store. I always enjoy those responses. :thumb
    #4
  5. Mobiker

    Mobiker Long timer

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    When my diode board failed, the generator light never went completely out. It would glow faintly. It ran fine, no cutting out, but then I turned around and hightailed it home as soon as noticed something was wrong.
    #5
  6. wirewrkr

    wirewrkr the thread-killer

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    Keep in mind that the coils are the first thing that people suspect on these bikes, but usually the last things that actually fail.
    It does happen, but RARELY.
    Check your ignition switch. while the bike is running, pull off the headlight lens and grab the back of the switch where the wires are attached and give it a wiggle, also do that to the key end as well.
    While wiggling listen for sounds of cutting out etc.
    The crimps on the switch bodies loosen up over the 30+ years that the bike has been around and can cause problems such as you've described.
    Also pull off the tank and check ALL connections on the harness for tightness and corrosion. ALL of them.
    Robert
    #6
  7. bmwloco

    bmwloco Long timer

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    #7
  8. wirewrkr

    wirewrkr the thread-killer

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    Rick never told me he'd hired a publicist.
    #8