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Thread: 1985 K100RS reducing/cancelling handlebar buzz

  1. #1

    1985 K100RS reducing/cancelling handlebar buzz

    I would like to address the handlebar buzz on my bike. I have re-torqued the engine mounting bolts. Clymer states 28-32 ft.lbs, so I torqued them to 30. My winter maintenance included removing the throttle body for cleaning, replacing all the rubbers (engine and air box side), all new fuel lines and vacuum lines and rubber plugs. I balanced the throttle body afterwards also.

    I popped off one of the grips and I have 15mm I.D. bars. I can get a used set of BMW OEM bar weights. What I would like to know is, are the bar weights effective?

    Thanks,
    Tom

  2. #2
    Quote Originally Posted by mcmlcccvrs View Post
    I would like to address the handlebar buzz on my bike. I have re-torqued the engine mounting bolts. Clymer states 28-32 ft.lbs, so I torqued them to 30. My winter maintenance included removing the throttle body for cleaning, replacing all the rubbers (engine and air box side), all new fuel lines and vacuum lines and rubber plugs. I balanced the throttle body afterwards also.

    I popped off one of the grips and I have 15mm I.D. bars. I can get a used set of BMW OEM bar weights. What I would like to know is, are the bar weights effective?

    Thanks,
    Tom
    Yes, bar weights are helpful.
    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://web.bigbend.net/~glaves/

  3. #3
    Liaison 20774's Avatar
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    One of the threads in the Similar Threads pane is about a buzz in a K75 bike...maybe some crossover there??
    Last edited by 98lee; 05-24-2020 at 12:56 AM.
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    '78 R100/7 & '69 R69S & '52 R25/2
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  4. #4
    Registered User kioolt's Avatar
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    You could try a product that I use on my 91 K100LT. It installs inside of the handlebars from end to end. I found this link for a similar product. http://www.barsnake.com/ I'm not sure if this is what is in mine since I installed mine over 28 years ago.
    2004 R1150RT 186,800 miles , 1991 K100LT 128,700 miles, 1982 R100RT 106,900 miles
    Total 422,400 BMW miles
    AMA,BMWRA,BMWMOA
    The cheapest thing on a BMW is the nut that connects the handlebars to the seat.

  5. #5
    3 Red Bricks
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    Quote Originally Posted by 20774 View Post
    One of the threads in the Similar Threads pane is about a buzz in a K75 bike...maybe some crossover there??
    No, a properly tuned K75 does not have handlebar buzz. A K100 does.



    LONG MAY YOUR BRICK FLY!

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    Lee Fulton Forum Moderator
    3 Marakesh Red K75Ss
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  6. #6
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    Quote Originally Posted by mcmlcccvrs View Post
    I would like to address the handlebar buzz on my bike. I have re-torqued the engine mounting bolts. Clymer states 28-32 ft.lbs, so I torqued them to 30. My winter maintenance included removing the throttle body for cleaning, replacing all the rubbers (engine and air box side), all new fuel lines and vacuum lines and rubber plugs. I balanced the throttle body afterwards also.

    I popped off one of the grips and I have 15mm I.D. bars. I can get a used set of BMW OEM bar weights. What I would like to know is, are the bar weights effective?

    Thanks,
    Tom



    Tom,


    The K100 had a buzzy engine. That is why they came with bar end weights (yours must have been removed), rubber mounted handlebars, and rubber mounted peg plates in an effort to smooth things out. If your bike does not have these, it is probable that they were removed by a previous owner.



    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

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

  7. #7
    A previous post mentioned a Bar Snake which is a lead bar that can be stuck inside the handlebars. This would work if the bike does NOT have heated grips. If it has heated grips the wiring is inside the bars and a Bar Snake will not work.
    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://web.bigbend.net/~glaves/

  8. #8
    That Bar Snake might be up for consideration. I don't have RS bars on my RS, so when the original bars went bye-bye, so did the bar end weights I suspect. What I have is about a 5" rise from top of the clamps to bar tips. RT's? I like the position although I don't know any different. Unheated grips by the way.

  9. #9
    Quote Originally Posted by mcmlcccvrs View Post
    That Bar Snake might be up for consideration. I don't have RS bars on my RS, so when the original bars went bye-bye, so did the bar end weights I suspect. What I have is about a 5" rise from top of the clamps to bar tips. RT's? I like the position although I don't know any different. Unheated grips by the way.
    In which case a Bar Snake would work nicely to damp vibrations.
    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://web.bigbend.net/~glaves/

  10. #10
    Registered User kioolt's Avatar
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    The barsnake that I have seen are not lead bars but is a long hard rubber solid tube that is pulled through the bars by a string/rope that is attached to one end. It stretches when being installed and once you quit pulling it will expand to fill the bar. It is then that you cut off the excess length.
    2004 R1150RT 186,800 miles , 1991 K100LT 128,700 miles, 1982 R100RT 106,900 miles
    Total 422,400 BMW miles
    AMA,BMWRA,BMWMOA
    The cheapest thing on a BMW is the nut that connects the handlebars to the seat.

  11. #11
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    85 K100RS w 203,000 miles: Bar Buzz at 4,000 RPM, unofficial improvements:

    I found that my bar buzz was tolerable, bike has bar weights and heated grips, no risers, stock screen, not much weight on my relaxed hands. I have and use the $8 BMW throttle locker screw underneath too, it holds throttle at whatever I set it.

    If mine buzzes extra, I change the spark plugs to 4 new ones from a dealer at a high price. The motor just loves new spark plugs, maybe every 12,000 miles. Careful wiggle and pull to get the ignition wires off.

    I also found that mine ran a little lean with the alcohol diluting the fuel, so I richened my mixture with the secret 5mm allen below the air filter about a sixth of a turn. The exhaust pipe runs a little blacker and the tank runs a few miles less but the engine runs as smoothly as it did on the rare occasion that I filled it with ethanol free gas.

    The injectors squirt a volume per firing, with ethanol having less power per liter than gas, the 10% mix will also have less power per liter, the hidden screw tells the injector to put in just a little more volume.

    Hope this helps

  12. #12
    Tell me more about this secret 5mm allen screw. Where exactly is the access and what does it do?

  13. #13
    Dances With Sheep GREGFEELER's Avatar
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    Lean drop methoid to adjust CO

    Quote Originally Posted by mcmlcccvrs View Post
    Tell me more about this secret 5mm allen screw. Where exactly is the access and what does it do?
    I've never thought of it as "secret" but likely many don't know the location of the classic K-bike CO adjustment. Just back from the top of the right corner of the air box (looking at the bike from the right side with the air tube removed), is a rubber plug you can locate with your fingers under the tank. Pulling that our carefully (don't lose it), give you Allen wrench access the the fuel system CO adjustment. To the best of my knowledge most K-bikes never get this checked, but IMO should as that fuel injection system doesn't have the ability to adjust for air pressure (elevation). There is a procedure described by the late Rob Lentini to set the correct CO level, he calls the "lean drop method." You adjust both the throttle body air bleed and the CO level. I have used this with great success and verified results with a CO meter. And, as you can see from the procedure, you can also set you bike a bit on the rich or lean side.



    By Rob Lentini
    '87 K75S
    Tucson, AZ
    K Whiner MC#11

    Here's a manual method of setting L-Jetronic K bike fuel injection CO (carbon monoxide) mixture without the need for an exhaust gas analyzer:
    1. Thoroughly warm the engine.

    2. Remove the rubber plug from the top right corner of the air box, above the engine. Using a 5mm allen, adjust the air flow meter idle air bypass screw under the plug for highest attainable idle speed. This should be about 1-2 turns out from the fully-seated position CW.

    3. Using a Carb Stix mercury manometer or vacuum gages, reset the butterfly bypass screws to resynchronize and establish an idle of 1050 rpm, or about one tach needle width above 1000 rpm.

    4. Now turn the idle air bypass screw CCW (from the top) until rpm is lowered by 50 rpm to 1000, about 4-5 total turns out. (This is called the lean drop method of setting CO, if you don't have an exhaust analyzer.)
    If you live above 4000 ft elevation, be sure to install the high altitude compensating plug into the harness. There's a receptacle taped to the frame on the left under the side panel.

    As a final check, you know you have done it all correctly when:

    1. You press the starter button with the engine running and the rpm stays the same or slightly increases (enriching signal to the computer).

    2. You pull out the high altitude plug and the rpm also increases (again, enrichening signal to the computer, but less so than the starter. You've set it lean, so enrichening will increase rpm).

    Don't forget to reinstall the rubber plug. I've also assumed you've got a 2 valve K with L-Jetronic injection. Motronic works differently. Have fun!
    Greg Feeler
    Ambassador & amateur K-Bike collector, it seems
    1972 R75/5, 1990 K75, 1990 K1, 1992 K75S, 2003 K1200RS

  14. #14
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    Air Fuel Mixture Screw

    My 1977 VW Dasher car (equalled Audi Fox) had this Bosch 5mm mixture adjustment screw as well, I fooled with that before getting my 85 K100RS in '95.

    You can adjust it, just by taking out the air filter with a right angle square tipped on the short end and long end allen wrench.

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