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Thread: 1985 K100 sudden loss of acceleration and super rich mixture smell from exhaust.

  1. #1
    Registered User dieselyoda's Avatar
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    1985 K100 sudden loss of acceleration and super rich mixture smell from exhaust.

    The bike runs nice, not great.

    History: old girl, about 80K miles, routine tune-ups, valves just checked, new plugs, one fuel pump/filter a few months ago.

    Up until lately, no complaints but suddenly got lazy and the exhaust smells super rich.

    Air filter is great, plugs look good, TB sync perfect, idles steady at 1000 RPM.

    My next thought is the timing changed and I have gone retarded a bit. Checked my marks with a strobe, marks align.

    Not sure where to go next except advance the timing and risk burning pistons/valves.
    1997 R1100RT, 1981 KZ 440 LTD, R80RT, R90/6 sidecar, K1100RS,1983 K100RS (Cafe now)

    “The major civilizing force in the world is not religion, it is sex.”

  2. #2
    3 Red Bricks
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    Yoda,


    Try this next. https://forums.bmwmoa.org/showthread...erature-sensor

    Don't advance the spark. That is not the problem.




    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

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

  3. #3
    I read the original post and my mind instantly suspected the engine temperature sensor. But I see Lee beat me to it.
    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/

  4. #4
    Registered User dieselyoda's Avatar
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    You guys are on to something. The sensor is working but seems lazy or the thermostat is stuck open.

    The engine isn't getting very hot, about 150 degrees but I am not sure the reason is the thermostat yet. Pretty low ambients here last few days.

    I am a little afraid to bring it up to temperature in my shop without a fan cooling the exhaust but I guess if I remove anything that could melt, I should be OK?
    1997 R1100RT, 1981 KZ 440 LTD, R80RT, R90/6 sidecar, K1100RS,1983 K100RS (Cafe now)

    “The major civilizing force in the world is not religion, it is sex.”

  5. #5
    3 Red Bricks
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    Lazy?

    Either the sensor exactly matches the water temp throughout the range or it doesn't. If it doesn't, it needs to be replaced. Use your infared temp gun to verify the water temp in the pan for different resistance readings.

    Usually you should remove the sensor and "bench test" it in a pan of varying temp water.

    If the sensor tests ok, clean the connections at the sensor and at the ECU with DeOxit. Any corrosion at the connections will vary the resistance seen by the ECU which will result in incorrect mixture.





    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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    Still could be the sensor but the thermostat is definitely not holding. Never gets hotter than 150F.

    Ordered a new thermostat, 4 weeks away!
    1997 R1100RT, 1981 KZ 440 LTD, R80RT, R90/6 sidecar, K1100RS,1983 K100RS (Cafe now)

    “The major civilizing force in the world is not religion, it is sex.”

  7. #7
    3 Red Bricks
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    In stock at EME: https://www.euromotoelectrics.com/pr...mostat-716.htm



    Don't forget to order the cover O-ring (under options) for $4.






    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

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

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