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  1. #1
    Registered User naddy100's Avatar
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    Some more diagnostic ideas

    http://www.nsaddy.net/Videos/Bike/Bike.html

    Recall that a few weeks ago I had a 1988 K100 that stumbled intermittently. It never died. It just stumbled. Based on that I kinda went down the fuel path. I replaced the fuel filter and replaced the fuel pump with a IBMWR-suggested non-BMW pump, complete with the shimming required to have it fit.

    It's quite possible that it only had some water in the tank. I don't think I know exactly what the original problem was, but it ran fine for a week or so and then it got worse.

    Now it doesn't run above an idle. The link shows what it's like. It's an mp4 file.

    I'm thinking of emptying the tank, putting the BMW fuel pump back in, and replacing the fuel filter again. The tank-to-fuel-rail line is relatively new. I haven't checked the fuel-rail-to-regulator line.

    A brief peek in the tank today and the non-BMW fuel pump is still in place.

    Ideas about how to diagnose why it won't run above an idle? I never put a fuel pressure gauge on the fuel line, so I don't know what pressure the system is producing.

    Noel
    Last edited by naddy100; 05-03-2010 at 03:19 AM.

  2. #2
    It soudns to be running extremely lean. Unplug the throtle switch to make sure the idle contact isn't the culprit-you can run the motor without it connected. If hat's not it, I would suspect the airflow meter. These began failing a few years ago.

  3. #3
    MichiganMike MICHIGANMIKE's Avatar
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    Air flow Meter

    A second here to check the Air Flow, I had a K75 with same symptoms and it was just the feed tube in the front was not secured properly.

  4. #4
    Firefighter Randy
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    Probably a foregone conclusion, however, did you have the high idle fully on?

  5. #5
    Registered User naddy100's Avatar
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    Quote Originally Posted by RNowell View Post


    Probably a foregone conclusion, however, did you have the high idle fully on?
    By 'high idle,' do you mean the choke? As I understand the choke, it just turns the rpms up a little. And, since I'm not Campbell Tellman (congratulations to Campbell!) I will probably start messing with it tomorrow.

    Noel

  6. #6
    Registered User naddy100's Avatar
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    http://nsaddy.net/PressureGauge/PressureGauge.html

    I unhooked the throttle switch and it made no difference.

    I hooked a fuel pressure gauge into the line at the front of the fuel rail. Here are the results. The reading oscillates between 32 and 38 psi, which seems to fit Clymers. This suggests that it isn't an obvious failure on the fuel side like fuel pump or fuel filter.

    Following lostboy and MichiganMike, I guess I next started on the air side, but that's pretty simple. Either the air flow meter is sitting correctly in the top of the air filter case or not. I pulled the air box and the air flow meter is where it's suppose to be. I guess the electronics could be bad. Hmm. I don't think I've ever changed the air filter. Would that cause something as drastic as this as suddenly (relatively) as this?

    I know there's always the possibility of those tubes being broken that run from the Air Plenum Chamber to the intake manifolds(?). I guess I figured the symptom would be rough running rather than inability to run above an idle.
    Last edited by naddy100; 05-07-2010 at 10:11 PM.

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