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Thread: 1994 K75S Z Hose Question

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  1. #1
    Slipster Slipster's Avatar
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    1994 K75S Z Hose Question

    Well I have been into the bike replacing rubber bits here and there. Just did a O Rings change in the starter, Alternator Monkey Nuts etc. etc. etc. I also found a tear in the Z hose. It ripped apart when I removed it. A new one is on the way. I cranked the bike over after putting it all back together again just to hear if the starter and alternator were ok. I had no Z hose installed. The bike starts but will not run.

    So my question is one of better understanding what the Z Hose actually does and how that little hose can prevent the motor from running ?? IMPORTANT little hose
    Expect The Unexpected

  2. #2
    3 Red Bricks
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    It will not run without the Crankcase vent hose (Z hose).

    The Crankcase vent hose does what its name implies. It vents the crankcase (into the intake plenum).

    It vents it into the plenum above the throttle bodies AFTER THE AIR FLOW METER. Any air that gets into the plenum is unmetered air, meaning that the computer does not know it is there and does not inject enough fuel to compensate for it. Therefore, the mixture is way too lean to properly run. A similar situation will happen if you have the hose in place and remove the oil filler cap (happens on most modern cars too).

    SMALL cracks in that hose will lean out the mixture enough to cause a multitude of problems (poor idle, burned valves, etc.) and that hose is VERY thin and in the hottest part of the bike. The cracks will happen just below the upper hose clamp and just above the lower hose clamp. These hoses usually require changing every couple years but need to be checked WAY more often ( at LEAST once a year).



    Last edited by 98lee; 11-21-2012 at 03:17 AM.
    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

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

  3. #3
    Slipster Slipster's Avatar
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    Thank you Lee for your detailed response to my question. I understand now and will definitely check the hose every year from here on out
    Expect The Unexpected

  4. #4
    Registered User kgadley01's Avatar
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    Thats good info...
    AKA SNAPGADGET
    Lifes too short to ride an ugly Motorcycle

  5. #5
    Registered User argent brick's Avatar
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    Quote Originally Posted by 98lee View Post
    It will not run without the Crankcase vent hose (Z hose).

    The Crankcase vent hose does what its name implies. It vents the crankcase (into the intake plenum).

    It vents it into the plenum above the throttle bodies AFTER THE AIR FLOW METER. Any air that gets into the plenum is unmetered air, meaning that the computer does not know it is there and does not inject enough fuel to compensate for it. Therefore, the mixture is way too lean to properly run. A similar situation will happen if you have the hose in place and remove the oil filler cap (happens on most modern cars too).

    SMALL cracks in that hose will lean out the mixture enough to cause a multitude of problems (poor idle, burned valves, etc.) and that hose is VERY thin and in the hottest part of the bike. The cracks will happen just below the upper hose clamp and just above the lower hose clamp. These hoses usually require changing every couple years but need to be checked WAY more often ( at LEAST once a year).
    Hey Lee,

    Mine has cracks in it. Do you have a part number?
    Lynn
    MOA #57883
    Current Ride: 1995 K75 Standard
    Past: 1978 Yamaha XS 750, 1976 BMW R60/6

  6. #6
    3 Red Bricks
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    11 15 1 460 480 VENT HOSE $15.56



    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

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

  7. #7
    Registered User argent brick's Avatar
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    Quote Originally Posted by 98lee View Post
    11 15 1 460 480 VENT HOSE $15.56
    Thanks, Lee.

    My BMW dealer is not that far away from the local VA hospital, and I figured that I would hit both in one trip, or so I thought. I dropped by the dealer to pick up the hose, and, of course, they did not have it in stock. They only keep one in stock and it was sold last week. Just my luck.
    Lynn
    MOA #57883
    Current Ride: 1995 K75 Standard
    Past: 1978 Yamaha XS 750, 1976 BMW R60/6

  8. #8
    BMW uber alles! Zagando's Avatar
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    I hope you ordered one, nonetheless! Among the best purchases one can make.
    ---Jeff

    ex: K75S Berlina R100GS/PD , K100RS , R75/5 , R60/2

  9. #9
    BMW uber alles! Zagando's Avatar
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    Quote Originally Posted by ARGENT BRICK View Post
    Hey Lee,

    Mine has cracks in it. Do you have a part number?
    Hey, Lynn; that might be part of the reason you are getting poor mpg as posted in your other thread.

    Mine was cracked as I discovered a couple months ago during another procedure---when I installed a new Z-hose it made a world of difference!
    ---Jeff

    ex: K75S Berlina R100GS/PD , K100RS , R75/5 , R60/2

  10. #10
    Dum vivimus vivamus ted's Avatar
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    A thread I started when I changed mine some time ago, with pics and replacement info
    http://www.bmwmoa.org/forum/showthread.php?t=56654

    A good lesson that these hoses may look fine but should still be changed with some regularity.
    Ted
    "A good stick is a good reason"
    1994 K75RT
    Moto Pages

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