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Thread: 1993 K75RT stumbles off idle

  1. #1
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    1993 K75RT stumbles off idle

    Anyone have a idea what would cause a lack of wanting to idle and the engine to stumble off idle. It sounds like it might have a miss at idle, when it idles.
    It runs fine at speed.
    I changed the plugs and drained and filled the tank. The exhaust temps are #1 735
    degrees and #2 around 550 and #3 around 625. The air filter is clean.

  2. #2
    3 Red Bricks
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    Three things that immediately come to mind; a cracked crankcase vent hose, cracked or missing vacuum caps on the throttle bodies, or exhausts valves too tight (this is actually my most likely guess).



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    Lee Fulton Forum Moderator
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  3. #3
    Rally Rat
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    +1 Lee

    Try balancing the throttle bodies too.

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    Quote Originally Posted by timtyler View Post

    Try balancing the throttle bodies too.
    AFTER adjusting the valves.



    LONG MAY YOUR BRICK FLY!

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    Lee Fulton Forum Moderator
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  5. #5
    Registered User argent brick's Avatar
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    Mine has been doing the same thing. I found that the vapor recovery line between the crankcase and the fuel tank was unpluged. Fixing that did not get rid of the problem but it did help.
    Lynn
    MOA #57883
    Current Ride: 1995 K75 Standard
    Past: 1978 Yamaha XS 750, 1976 BMW R60/6

  6. #6
    A bozo on the bus deilenberger's Avatar
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    Quote Originally Posted by argent brick View Post
    Mine has been doing the same thing. I found that the vapor recovery line between the crankcase and the fuel tank was unpluged. Fixing that did not get rid of the problem but it did help.
    That connection shouldn't be made. It was disconnected by BMW, and the fitting into the crankcase should have a rubber cap on it. The tank vent should go to the little funnel on the frame (provides an air gap and allows R&R of the tank much more easily) and from there to ground.

    You may want to look into that..
    Don Eilenberger http://www.eilenberger.net
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  7. #7
    Dum vivimus vivamus ted's Avatar
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    Often with these aging machines one thing may not be noticeable, it is when two or three things happen they do become noticeable. What you are describing sounds like it could be unmetered air entering the system. Usually the culprit is the crankcase breather hose - even if it looks fine it very well may be split all around the hose clamp (like mine was - search the forum for my photos...). There is a great piece out in teh Internets called "falschluft". If you google that you will have a great study in air leaks, just make sure to either speak German or use google translate. Edit- here it is:
    http://www.flyingbrick.de/pdf/Falschluft.pdf

    For me, replacing the vacuum buds, which i noticed were split once I got them off and looked at them, and the breather hose, made a world of difference. As an aside, the oem breather hose is more expensive but is well made and reportedly fits much better than the aftermarket ones.
    Ted
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  8. #8
    Registered User argent brick's Avatar
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    Quote Originally Posted by deilenberger View Post
    That connection shouldn't be made. It was disconnected by BMW, and the fitting into the crankcase should have a rubber cap on it. The tank vent should go to the little funnel on the frame (provides an air gap and allows R&R of the tank much more easily) and from there to ground.

    You may want to look into that..
    When you say "little funnel" do you mean the mean the air cup that clips onto the right side of the frame near the back of the tank? I found the vacuum leak when I pulled the tank to install one of those. My crankcase had about 10 inches of hose and no rubber cap. Now that it is plugged, my bike starts and idles better than ever before. My bike has never run super smooth so I can't help but wonder if the PO sold it to me like that.

    Going for a ride this weekend. First real chance to go anyplace now that the vacuum leak is plugged. Get to see if there is any change in fuel economy.
    Lynn
    MOA #57883
    Current Ride: 1995 K75 Standard
    Past: 1978 Yamaha XS 750, 1976 BMW R60/6

  9. #9
    3 Red Bricks
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    Lynn,

    I would STRONGLY recommend that you check your valve adjustment.

    I just worked on a bike that had the nipple on top of the block, that used to be connected to that tank vent hose, uncapped. It burnt an exhaust valve (from running too lean) within 20,000 miles of a dealer valve adjustment. Then after replacing the head and valves, the valves were dangerously tight after only 4,000 miles. He brought it to me and I discovered the uncapped nipple. Check your valves!



    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

    Lee Fulton Forum Moderator
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  10. #10
    Registered User argent brick's Avatar
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    Quote Originally Posted by 98lee View Post
    Lynn,

    I would STRONGLY recommend that you check your valve adjustment.

    I just worked on a bike that had the nipple on top of the block, that used to be connected to that tank vent hose, uncapped. It burnt an exhaust valve (from running too lean) within 20,000 miles of a dealer valve adjustment. Then after replacing the head and valves, the valves were dangerously tight after only 4,000 miles. He brought it to me and I discovered the uncapped nipple. Check your valves!



    THANK YOU, LEE!

    What tools(and parts) do I need to check my valve adjustment?

    Thanx again Lee. YOU THE MAN!
    Lynn
    MOA #57883
    Current Ride: 1995 K75 Standard
    Past: 1978 Yamaha XS 750, 1976 BMW R60/6

  11. #11
    Slipster Slipster's Avatar
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    Is the Funnel and Hose / Cap unique to earlier Ks or was it prevalent throughout all production years?
    Expect The Unexpected

  12. #12
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    Quote Originally Posted by argent brick View Post

    What tools(and parts) do I need to check my valve adjustment?
    Feeler gauges and I would STRONGLY suggest an INCH/lb torque wrench for tightening the valve cover bolts (VERY easy to overtighten and strip the cylinder head threads 6 ft/lb = 72 in/lb) and new valve cover bolt bushings: 11 14 1 460 934 BUSH $0.73 ea. (10 required).

    You MIGHT also want to replace the two valve cover gaskets so that you know that they are fresh and will last through the next several valve adjustments/checks: 11 12 1 460 622 GASKET $8.82
    11 12 1 460 623 GASKET $8.82


    Check must be done with engine COLD (below 96 degrees).

    The comment in another thread about not removing the spark plugs only applies to the 4valve per cylinder bikes. Personally, I don't remove the plugs. I use the starter button with one hand and the kill switch with the other hand to turn the engine over to the next pair of valves to adjust. K75s will always stop with one intake and anothe exhaust in the correct position to adjust if the plugs are left in and bumped with the starter. BE QUICK with the kill switch or it will start and get oil everywhere!!!


    Intakes should be .006"-.008". Exhausts should be .010"-.012" with .012" being strongly prefered. Shims come in .05mm (approx. .002") increments.

    Make a chart showing the current clearances with date and mileage. If they are good, keep these #s in your files for future reference. If they are not all good, put the valve cover back on until you make arrangements to have them adjusted. You have several choices (dealer, buy adjustment tools and shims and do it yourself, or bring the bike to me).



    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

    Lee Fulton Forum Moderator
    3 Marakesh Red K75Ss
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  13. #13
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    Quote Originally Posted by Slipster View Post
    Is the Funnel and Hose / Cap unique to earlier Ks or was it prevalent throughout all production years?
    The "funnel"/"cup" (actually called an Air Accumulator by BMW) 16 13 2 307 467 AIR ACCUMULATOR $2.26 was used on most non-US Bricks through the K1100.

    It was used only on the two valve US bikes and I believe that it was not used on California bikes (can't let those gas fumes get into our air). But since these bikes are so old and have moved around the country and been modified so much, the only sure way to know what is there is to look. Some people did not do the modification correctly, so the presence of the cup does not mean that the crankcase nipple is properly capped, and visa versa.



    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

    Lee Fulton Forum Moderator
    3 Marakesh Red K75Ss
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  14. #14
    Slipster Slipster's Avatar
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    Quote Originally Posted by 98lee View Post
    The "funnel"/"cup" (actually called an Air Accumulator by BMW) 16 13 2 307 467 AIR ACCUMULATOR $2.26 was used on most non-US Bricks through the K1100.

    It was used only on the two valve US bikes and I believe that it was not used on California bikes (can't let those gas fumes get into our air). But since these bikes are so old and have moved around the country and been modified so much, the only sure way to know what is there is to look. Some people did not do the modification correctly, so the presence of the cup does not mean that the crankcase nipple is properly capped, and visa versa.




    Thanks Lee. Do you have a pic or a pointer of where this nipple is? Just a minds eye view of where I start looking
    Expect The Unexpected

  15. #15
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    Quote Originally Posted by Slipster View Post
    Thanks Lee. Do you have a pic or a pointer of where this nipple is? Just a minds eye view of where I start looking
    Remove the air intake snorkle from the right side of the air box (just pulls out). Look at the very top, front, center of the engine block directly below the fan motor. There is a 3/4" tall by about 3/16" diameter nipple just at the parting line with the timing chain cover.

    This nipple SHOULD be capped as part of the conversion to the tank venting going into the air accumulator.




    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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