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Thread: '91 K75S starts but won't keep running, or restart?

  1. #16
    Registered User AntonLargiader's Avatar
    Join Date
    Jul 2004
    Charlottesville, VA
    First I would throw new plugs in it just because I'd want everything to be as perfect as possible. It has helped SO many times that it's not worth thinking about whether or not it "should."

    Then check the S-shaped hose and general condition of the rest of the intake stuff.

    How old is the fuel?

    Lastly, I had a problem with a K75 one time where the bike would fire up and immediately die, every time, but it was like half a second rather than three or four. The details are a bit fuzzy but it turned out to be a bad ignition module that would drop power on one pin (to the fuel pump I think) as soon as the engine caught. I think I fixed it by bypassing whatever pin it was. It was a very interesting problem to find. I don't suspect this is your problem but if it turns out that you are losing spark after some engine cranking then you could have something similar going on.
    Anton Largiader 72724
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    Virginia Motorrad Werkstatt BMW motorcycle service and repair in central Virginia

  2. #17
    Registered User
    Join Date
    May 2008
    Western Massachusetts
    Anton's reply raised a few questions in my mind.
    You checked the plugs for spark at one point. Presumably the bike was in the "will start then quit" mode at that point.
    When the bike is in the "quit and won't restart" mode, do you still have spark?

    I'd give it a test under those conditions, if you haven't already, as lack of spark under those conditions gives you a direction to pursue.

  3. #18
    Join Date
    Mar 2010
    Akron, Ohio
    I hadn't looked at the thread for a while, but thought I would check back in to update the situation.

    First off, I would like to apologize for my somewhat cranky last post. As all of you can imagine, after putting in all these new parts, all the money it cost, and then have this bike start then stop, well, I guess you can imagine my frustration. I blame myself for getting into this situation in the first place. The bike had sat for years, I thought I could save the little guy, and it was pretty cheap. All bad ideas. Live and learn...again. I do not foresee rebuilding another neglected BMW, (my third now.) My R1100RT was not cheap, and was very well maintained over the years by an MOA member. Of course, it has never given me any trouble. I believe the connection has finally been made for me.

    Second, I want to sincerely thank those of you who have tried to help. It has restored my faith in being a member of the MOA. I'm not riding 30,000 miles a year, or buying a new GSA every few years. But people here still do their best to help. That's appreciated.

    Lastly, many of you were right about the problem. I did some checking on posts and found that the K75 engines have a reputation for flooding. Also, that once flooded, the plugs are often ruined. This seemed contrary to fifty or so years of auto repair, but I had little to loose. As a final attempt at repair before hauling it to a dealer, I replaced the hardly used plugs(Bosch) with a new set of NGKs which had been recommended here on the forum. The bike started instantly. I will now continue to re-do the body work, recover the seat, etc to finish the project. The K75Ss are beautiful bikes, so, I hope it's worth it.

    Thanks again to all of you for the patience and assistance.

  4. #19
    Registered User drneo66's Avatar
    Join Date
    Jun 2009
    Rochester, MN
    Quote Originally Posted by jconway607 View Post
    I do not foresee rebuilding another neglected BMW, (my third now.)
    You say that now... but I think you'll have a hard time wiping that smile off your face the first time you go out and exercise the throttle.
    Current: 2007 BMW R1200RT
    Former: 1995 BMW K75S, 2009 BMW G650GS
    MOA Member #:150400, IBA#: 37558

  5. #20
    3 Red Bricks
    Join Date
    Jan 2007
    Pleasanton, Ca.
    Quote Originally Posted by jconway607 View Post
    Yes, it looks like this "incredibly reliable" k75 will need some incredibly expensive diagnostics and parts.

    Meanwhile, my 1994 Honda Pacific Coast starts every time. Now why is that?

    See, that wasn't so expensive now, was it?

    You probably killed the plugs with the short runs in the garage every month. The plugs never got a chance to run clean. Get that thing ridable and it will put that Honda to shame.


    Ride Safe, Ride Far, Ride Often

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

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