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Thread: 87 K75S Quit Running

  1. #1
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    87 K75S Quit Running

    Went out for a ride Saturday afternoon, got less than a mile from home when the bike "backfired" loudly & quit. I pulled in the clutch & it started right up but immediately quit. I was able to coast home (thankfully it quit at the top of a hill) & started it again slowly reving the engine, as it approached 3K RPM the tach slowly started drifting down while the engine continued to rev before suddenly quitting. I started it once again then shut it off. My initial thought is the HES but haven't had a chance to work on it since this happened.

    Don't know if this is related but going to work & on the ride home Friday my charge indicator kept flashing while I was riding but would go out while stopped and idling for traffic or stop light the flashing stopped. A separate voltage indicator remained green throughout the ride.

    Other than changing all the fluids & installing a set of tires in early June I haven't done anything other than ride it.

    Any ideas?
    lostandwandering
    87 K75S
    previous 2008 R1200R

  2. #2
    Registered User drneo66's Avatar
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    Someone much smarter than me will chime in soon, but I would check your battery/transmission ground as well as look at all your fuses. It's the easy and cheap thing to do first.
    1995 BMW K75s - 100k and climbing!
    2007 BMW R1200RT - 62k
    2009 BMW G650GS - 22k and ready for Alaska!

  3. #3
    Registered User mlytle's Avatar
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    start with all the basic electrical tests...battery, grounds and alt. the charge light coming on is a clue....
    Marshall
    92 K75s
    94 K75s
    09 K1300s

  4. #4
    3 Red Bricks
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    87s have a very small battery to transmission ground wire. Check it for possible broken strands. Later years receive a larger gage wire. You may want to try running a second parallel 12 gage ground wire and see if that helps.

    If you get ambitious, clean the frame ground wire connections on the left side of the center frame tube under the gas tank and run a 12 gage wire from that bolt to the transmission ground bolt.



    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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    Other areas to check:

    Check brush length in alternator

    Clean contacts inside ignition switch and kill switch

    Clean brushes and commutator inside starter

    Unplug and replug the connector to the ECU several times





    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

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

  6. #6
    Bear with me a minute. A loud bang backfire indicates a buildup of fuel in the exhaust then ignited. Classic backfire in the exhaust. This argues loudly that there was erratic ignition. Start chasing it from that premise.
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://web.bigbend.net/~glaves/

  7. #7
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    Checked so far

    Finally got a chance to do some preliminary checks. Wiring & grounds look good, battery connections solid. Installed a tested ECU, the only change is that now it won't start at all. What triggers the HES? There doesn't appear to be anything behind the magnets to create a change. This may be a dumb question but I never had the need to inspect what was behind that cover before. The Clymer manual shows a disk behind the magnet plate that I don't see on mine.
    lostandwandering
    87 K75S
    previous 2008 R1200R

  8. #8
    3 Red Bricks
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    Pull a spark plug. Number 3 works best because it has the longest wire. Plug it scurely into the plug wire. Positively ground the threaded end of the plug. I like to use a jumper wire with alligator clips from the ground bolt on the transmission to the ground electrode (the L shaped part) of the plug. Turn on bike and crank to see if you have spark.

    If you have spark, insure that the pump is running. Remove filler cap and listen for pump running for a second or two after you let off starter button. You should also see turbulence in the front right section of the tank from the fuel regulator return.





    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

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

  9. #9
    Registered User
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    Quit running

    Lee,

    I got spark & the fuel pump runs. It started once today, ran briefly then just quit again. I've swapped out the injector control & ignition controls.
    lostandwandering
    87 K75S
    previous 2008 R1200R

  10. #10
    3 Red Bricks
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    Did the headlight remain on when it quit?

    Are the spark plugs wet?




    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

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

  11. #11
    3 Red Bricks
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    Also look for large vacuum leaks:

    Vacuum caps at throttle bodies

    Vacuum hose to fuel pressure regulator (disconnect from #3 throttle body, suck aaccume on it, put your tongue over the end and see if it holds)

    Crankcase vent hose

    Nipple at top front of engine block just below fan (pull off air intake snorkle to get a good look at it)

    Check the 2 1/2" diameter 90 degree hose between the air filter box and the intake plenum for a tear




    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

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

  12. #12
    Still plays with trains. tinytrains's Avatar
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    Check that the fuel pump connector to the tank is clean and tight. They loosen up with age, and can go intermittent.

    What is your battery voltage, static and cranking? Just because it is sparks, does not mean it sparks at the right time.

    Oh, and have you checked the fuel filter? I had one plug up solid once, but there was nothing in it. The paper varnished. Try blowing through it.

    Good luck.
    Scott
    1988 K75 Low Seat
    2009 R1200R Roadster

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