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Thread: 1987 K75S, wonky tach.

  1. #1
    Registered User dieselyoda's Avatar
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    1987 K75S, wonky tach.

    I'm getting closer to getting this boat anchor back to form. I got all the wiring and electrical systems working and was ready for a start up. She fired up quite nicely without the high idle lever and stumbled with good blue smoke. I was fine with that.

    Checked my tach, steady at 2000 RPM. I guessed I was about 1000 RPM. After the smoke cleared and she was running very nicely, tach at 2000 RPM.

    A little throttle, no change. A bit more throttle, the needle jumps and won't settle.

    Confirm the tach isn't anywhere close to real RPM. Confirm that my #1 coil isn't breaking frequency. Check my grounds, less than 0.1 ohms everywhere. Confirm my alternator light comes on, part of the circuit as I see it.

    Now I'm thinking I have a bad tach head.

    What do I do know?

    She is a babe and a ton of fun but I'm getting a bit frustrated with all the ghosts.
    1997 R1100RT (Restored Basket Case) , 1981 KZ 440 LTD (Restored Basket Case)
    1986 K75S(the beutch), 1993 K1100RS (blown engine), 1997 Chev Short Box (4x4 with an LT1)
    "You can easily judge the character of a man by how he treats those who can do nothing for him."

  2. #2
    3 Red Bricks
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    Yoda,

    Sounds kind of like a ground problem. First thing I would do is clean the main grounding bundle under the gas tank on the center frame rail. And obviously the ground cable from the battery to the transmission.

    While I don't know offhand what might be causing your problem, bad/oxidized connections are common on these old bikes.

    I would also look at the multi pin connectors at the back of the instrument cluster. These have square pins. Sometimes it helps to take some needle nosed pliers and give each pin a slight twist. This causes the corners of the pins to dig into a different spot in the socket and gives a tighter fit.

    Also, the early K instrument clusters suffered from moisture/condensation problems. The tach (and other components) each plug into the internal cluster circuit board with similar square pins.


    Flakey electrical/electronic problems are SO much fun to chase!



    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

    Lee Fulton Forum Moderator
    3 Marakesh Red K75Ss
    Mine, Hers, Spare

  3. #3
    Registered User dieselyoda's Avatar
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    As one of my old bosses drilled into my head, "grounds, grounds and then check them again". I'm pretty confidant that I'm not dealing with a ground problem.

    I see that Capital Cycle sells just a tach head, pricey though. Does that imply the tach head is serviceable to a point?

    The whole harness has been apart once and cleaned up but I have to do it again because I don't have a brake light from the front brakes and the switch closes.
    1997 R1100RT (Restored Basket Case) , 1981 KZ 440 LTD (Restored Basket Case)
    1986 K75S(the beutch), 1993 K1100RS (blown engine), 1997 Chev Short Box (4x4 with an LT1)
    "You can easily judge the character of a man by how he treats those who can do nothing for him."

  4. #4
    3 Red Bricks
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    The new tach head lists for $556 from any BMW dealer. I would NEVER go that way. That's IF the problem is in the cluster. I would still open the cluster and check the tach head connecting pins (clean and twist) inside. Replace the gasket on the housing while it is apart.

    Used complete clusters can be had for $100-200. Just get a guarantee that everything works or it can be returned before you buy.



    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

    Lee Fulton Forum Moderator
    3 Marakesh Red K75Ss
    Mine, Hers, Spare

  5. #5
    3 Red Bricks
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    Quote Originally Posted by dieselyoda View Post

    The whole harness has been apart once and cleaned up but I have to do it again because I don't have a brake light from the front brakes and the switch closes.
    You might want to check the connection at the bulb monitoring relay in the relay box under the tank. End pin E1. Other end E2 is from the rear switch.



    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

    Lee Fulton Forum Moderator
    3 Marakesh Red K75Ss
    Mine, Hers, Spare

  6. #6
    Registered User dieselyoda's Avatar
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    Quote Originally Posted by 98lee View Post
    The new tach head lists for $556 from any BMW dealer. I would NEVER go that way. That's IF the problem is in the cluster. I would still open the cluster and check the tach head connecting pins (clean and twist) inside. Replace the gasket on the housing while it is apart.

    Used complete clusters can be had for $100-200. Just get a guarantee that everything works or it can be returned before you buy.




    OOOOHHHHH, inside....................

    Crap, the closer I get to finishing this thing, yet another thing.
    1997 R1100RT (Restored Basket Case) , 1981 KZ 440 LTD (Restored Basket Case)
    1986 K75S(the beutch), 1993 K1100RS (blown engine), 1997 Chev Short Box (4x4 with an LT1)
    "You can easily judge the character of a man by how he treats those who can do nothing for him."

  7. #7
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    Quote Originally Posted by dieselyoda View Post
    OOOOHHHHH, inside....................

    Crap, the closer I get to finishing this thing, yet another thing.
    If you finished it, you wouldn't have anything to do. That could get boring. Nothing but riding.

    At least they're not Lucas electrics!



    That's why Lucas invented automotive electrics, to keep the Brits from getting complacent.

    Lucas, the Prince of Darkness

    The Lucas motto: Get home before dark

    Lucas, the inventor of the dead short

    The three positions on a British headlight switch: Dim, Flicker, Off

    Lucas, the inventor of the first intermittent wiper

    Lucas, the inventor of the first self dimming headlight

    The reason British drink warm beer: Lucas refrigerators

    smoke.jpg




    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

    Lee Fulton Forum Moderator
    3 Marakesh Red K75Ss
    Mine, Hers, Spare

  8. #8
    Registered User dieselyoda's Avatar
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    I know why the British don't make computers; they can't make them leak oil.

    I gotta get me a jar of universal replacement smoke.
    1997 R1100RT (Restored Basket Case) , 1981 KZ 440 LTD (Restored Basket Case)
    1986 K75S(the beutch), 1993 K1100RS (blown engine), 1997 Chev Short Box (4x4 with an LT1)
    "You can easily judge the character of a man by how he treats those who can do nothing for him."

  9. #9
    Registered User kentuvman's Avatar
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    I had a positive experience with Rick at Overseas Speedometer in Austin TX - he is very familiar with the K cluster & honest & fair.
    Ken Tuvman
    Excelsior, MN
    K75s, R65LS, R60/5

  10. #10
    3 Red Bricks
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    Quote Originally Posted by dieselyoda View Post

    I gotta get me a jar of universal replacement smoke.
    Since the Lucas stuff is, by nature, twice as thick, you only need half the specified amount in Bosch systems.




    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

    Lee Fulton Forum Moderator
    3 Marakesh Red K75Ss
    Mine, Hers, Spare

  11. #11
    Registered User dieselyoda's Avatar
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    I'm 99% finished, almost ready for a test drive.

    Sooooooooo, I followed the suggestions here. Took the head all apart, cleaned up everything, turned the green stuff to shiny and now, no tach.

    What am I missing?
    1997 R1100RT (Restored Basket Case) , 1981 KZ 440 LTD (Restored Basket Case)
    1986 K75S(the beutch), 1993 K1100RS (blown engine), 1997 Chev Short Box (4x4 with an LT1)
    "You can easily judge the character of a man by how he treats those who can do nothing for him."

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