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Thread: k75 running ruff, wants to die

  1. #1
    chuck_donahue
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    k75 running ruff, wants to die

    Well the new k75s trans is shifting fine now< but it is running real ruff.

    It starts right up, idels good, but when you go to give it gas it wants to die. If yo give it very little gas very slowly you can keep it running. It has a hard time getting above 6000 rpm and spits and sputters.

    So looking, i unpluged the tbs thinking that it should change how it is running. no change what so ever. is there a way to test it.

    I did drive the bike before I did the trans repair, and I think it ran good, so maybe cleaning the throtle bodies, and all on area around there i messed something up cleaned up the motor.

    Any Ideas.
    Chuck

  2. #2
    chuck_donahue
    Guest
    I just took it for a 20 mile ride. now it has a hard time getting above 4000 rpm. I went to the bmw dealer by me (I am one of the lucky few that has a dealer in the next town over) I am going to pull the injectors and check the spray. If that is ok I am going to look at the coils.

    Anyone have any other ideas.

    It starts up great, idles good and smoth. give it gass it falls flat on its face.

    chuck

  3. #3
    kayseventyfive
    Guest
    I would tee in a fuel pressure gauge and watch it as you power up on the road. That would tell the tale on fuel pump and filter suspicions.

    A bottle of Red Line Fuel Cleaner or Seafoam could save you the effort of removing and cleaning the injectors. I have had good results with both, but Red Line seems to work faster.

    .

  4. #4
    Registered User breyfogle's Avatar
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    If it starts and idles OK, but doesn't pull RPM, I would be looking at the fuel filter, the airflow meter assembly, and maybe the ignition control unit.
    '89 K75S Original Owner
    '94 (Beta) R11RS, ( RIP 12-5-2010 courtesy of blind left turning cage driver ) ....

  5. #5
    Mars needs women! 35634's Avatar
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    +1 on the fuel filter. Check that first.
    1987 K75S
    Original litter
    Original owner
    2012 Ural Gear Up

  6. #6
    Benchwrenching PGlaves's Avatar
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    The TPS on a K75 is just a 3 way switch:

    Throttle closed

    Off

    Wide Open Throttle

    It signals the LJetronic to shut of the injectors if RPM > 2,000 and the throttle is fully closed (as in coasting or decelerating sharply).

    It signals the Ljetronic to add fuel when the throttle is wide open.

    And most of the time - between off and WFO - it does nothing.

    It sounds like it is either starving for fuel (pressure and injectors) or starving for air (air cleaner). I'd check the injectors and the air cleaner. Look for mice nests too.

    There is a possibility too, that it is computer related. Try unseating and re-seating the connector to the LJetronic. Make sure those contacts are clean.

    There is a very slim possibility that the air sensor has failed.
    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://www.bigbend.net/users/glaves

  7. #7
    chuck_donahue
    Guest
    Thanks for the ideas.

    I took of the gas cap and noticed its using alot of fuel. just under 100 miles and only about 1/4 tank left, my other K75 gets 200 miles to a tank. Today I will change the tank from my other k75, see what that does, if that does nothing then I am going to try changing the coils. But 1st it gets new spark plugs.

    No air box for a mouse nest, it has that lufty exhaust with the air box gone and a k&N filter. I just got an air box so that is going back on I think. I have an extra air flo meter, jettronic, I also have the stock exhaust that will be going back on soon too.

    I will post when I find the problem.
    And again thanks for all the ideas.

  8. #8
    A bozo on the bus deilenberger's Avatar
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    Quote Originally Posted by chuck_donahue View Post
    Thanks for the ideas.

    I took of the gas cap and noticed its using alot of fuel. just under 100 miles and only about 1/4 tank left, my other K75 gets 200 miles to a tank. Today I will change the tank from my other k75, see what that does, if that does nothing then I am going to try changing the coils. But 1st it gets new spark plugs.

    No air box for a mouse nest, it has that lufty exhaust with the air box gone and a k&N filter. I just got an air box so that is going back on I think. I have an extra air flo meter, jettronic, I also have the stock exhaust that will be going back on soon too.

    I will post when I find the problem.
    And again thanks for all the ideas.
    Chuck, somehow I don't think the tank is the problem. The fuel filter is always suspect#1 when having running problems on a K.. one load of crap gas can turn it from a filter into a brick in minutes. Unless it's running rough, I doubt if plugs or coils is your problem.

    Perhaps some checking for basics might help. Have you tried disconnecting the vacuum hose to the fuel pressure regulator while it's idling? If there is no change in engine speed, I'd be checking the fuel pressure at the injector rail. Have you checked for intake leaks - like the Z shaped crankcase vent hose (although without an airbox - it's not clear to me that you'd have this hose, or if you did, where it's connected.) Have you done a high speed run/chop - and read the plugs? That will tell you quickly if the engine is running too rich or too lean.
    Don Eilenberger http://www.eilenberger.net
    Spring Lk Heights NJ NJ Shore BMW Riders New Sweden BMW Riders
    '07 R1200R (current ride) and some bimmers.. and a Porsche

  9. #9
    chuck_donahue
    Guest
    Well, I took the tank off my good running k75 and put it on the bad running k75, good pump, good filter, no change,

    Then I got rid of the K&N air filter, Put the air box back, (it had no air box just the K&N luftmiser setup) no change

    Then I changed the coils, no change, then the spark plug wires, oh and I put new plugs in too. no change.

    then I puit in new injectors ..... BINGO runs like it should.

    Thanks to all that helped me figure this out.

    Chuck

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