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    #1

    Non GS electrical problem

    Hi,

    I have a 1979 CB750K that won't hold a charge. I performed the resistance/continuity tests on the rotor, stator, and regulator/rectifier that the shop manual explains, but they all seem to be fine. I'm pretty sure the battery is fine, because when charged by the battery charger, it has no problem starting the bike after it has been sitting for a few months (read: starter off and on for a few minutes before the thing fires up). With everything off, I measure 12.5v at the battery. At idle, 11.8v, and at about 4000 rpm 12.4v. It won't go past about 12.4 volts no matter how high the engine is revved. Any ideas?

    Thanks
    Richard
    Tags: None
    #2
    Not familiar with the electrics you have, so I don't know which wires you should test, but it appears you need either a new stator or regulator. An output to the battery of 12.4 volts is enough to keep you running, but not quite enough to keep the battery charged, and any additional electric load will have to draw on battery reserves.

    Before replacing anything, you might try cleaning up all your connections, including the ground, same as you do on Suzukis. Clean connections could give you an extra 1/2 volt or even a bit more.
    Bertrand Russell: 'Men are born ignorant, not stupid. They are made stupid by education.'

    ​

    Comment

      #3
      Everything sounds about normal to me. I would check batttery ground, and particular regulator/rectifier ground. If there is not a case ground on the R/R, I would add one. Also, be sure and check the fuse box as those clips are prone to developing resistance too.

      Earl
      Komorebi-The light filtering through the trees.

      I would rather sit on a pumpkin and have it all to myself than be crowded on a velvet cushion. H.D.T.

      Comment

        #4
        I'm not sure how your 750 is wired but, the system used on my 78 CB550 has a field coil (controlled by a mechanical switch in the voltage regulator) that boosts the magnetic field at the stator. My manual does not provide a way to test the voltage regulator independant of the system. The voltages you stated seemed rather low. A chart in my manual suggests 12V at 1000rpm, 12.4V at 2000rpm, 13.2V at 3000rpm, and 14.5V from 4000rpm upward.

        Before the stator totally cashed in on my 78 GS1000, the battery would discharge when running with the lights on (even after bypassing the stator lead that goes through the light switch), but kept the charge with the lights off. There was some variation in resistance readings across the stator leads but I don't remember it as initially being a lot. When the stator finally gave up (wouldn't charge no matter how much I kicked it and swore at it) the resistance across two of the possible three lead tests dropped to almost zero (it was fried).

        So what I'm saying is: A small differance in resistance across the alternator leads may initially not SEEM to be significant, but could mean that only a few wraps of the stator are shorting. If this is the case it will only get worse not better. If I were you I would test the stator again. If you are convinced that the readings are OK, its something in the rest of the system.

        Good luck!

        Comment

          #5
          I have measured as much as a 2.5v drop between the voltage available at the battery and the voltage that was reaching the coils on my 750 after traveling through the harness, connectors, switches etc. Simply checking voltages point to point through the system and cleaning connections resulted in a gain of 2v at the coilsl, or a net loss of only .5v in the system.

          Earl
          Komorebi-The light filtering through the trees.

          I would rather sit on a pumpkin and have it all to myself than be crowded on a velvet cushion. H.D.T.

          Comment

            #6
            I have measured as much as a 2.5v drop between the voltage available at the battery and the voltage that was reaching the coils on my 750 after traveling through the harness, connectors, switches etc. Simply checking voltages point to point through the system and cleaning connections resulted in a gain of 2v at the coilsl, or a net loss of only .5v in the system.

            Earl
            I've noticed that also, Earl. There was a significant voltage drop though the ignition switch on one of my bikes. It only takes one bad connection to ruin your whole day!

            Comment

              #7
              Disconnect the stator wires. Run the bike and check the AC voltage of the stator to determin the condition of the stator should read minimun
              60-70 Volts AC at 4-5K RPM Check between the different leads. If there is a great difference from one lead to the next or an extreamly low reading. The the stator is toast. If the stator checks out and you have cleaned the connections to no avail It's time to replace the Rec/Reg

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