Page 1 of 2 1 2 LastLast
Results 1 to 15 of 16

Thread: 1985 K100RS Problems

  1. #1
    Registered User
    Join Date
    Nov 2008
    Posts
    61

    1985 K100RS Problems

    Good morning everyone.
    1. It seems that I need a long time to warm up my bike in the morning, have to keep the choke on for about five minutes. Then the bike's RPM reaches from 1500 to almost 3000 in idle at all of sudden. I have to turn off the choke, because I think the RPM is too high for its idle. But the engine will be off as soon as I turn off the choke. So I have to hold my throttle a little bit and keep the RPM under 2000 for another a couple of minutes, otherwise it will die at traffic lights if I ride it.
    2. After coming back from the rally last year, I replaced fuel filter, a damper and two fuel hoses from tank to the rail. But the bike uses much more gas than before. I remembered that I could ride almost two hundred mile with a full tank. But now, less than 150 miles I have to fill it up.
    I replaced spark plugs, ignition wires, thermostat about 30.000 miles ago. Replacing air filter every 20.000 miles and changing motor oil every 3000 miles. I always use BMW original parts and I really don't know what causes the problems.
    The bike is only 47.000 miles on it. Is it suppose to be like that because of the bike's age?
    Anyone has some ideas what's going on here?
    Thanks in advance.

    Sinclair Niu
    _____________
    Enjoy Riding and Ride Safe
    Sinclair & Mona Hamilton, NJ
    84 Honda Magna 500 / 85 BMW K100RS / K1200LT Will Be Next

  2. #2
    Registered User Beemer01's Avatar
    Join Date
    Mar 2007
    Location
    Chicago, Ill
    Posts
    975

    This sounds like a fuel or hose leak problem

    On these old K bikes - and I owned one for years - air for combustion is seldom the issue. It doesn't sound like a spark problem......

    You seem to have addressed the fuel angle and unless the injectors got clogged - let's look for a leaking hose. There is a breather hose - leaks here cause significant problems and after nearly 30 years yours would seem about due to expire.

  3. #3
    Registered User
    Join Date
    Nov 2009
    Location
    Phila
    Posts
    49

    Low mileage on K100RS

    Mine had low mileage around 100,000 mi.

    Fuel pressure was way too high, Dealer found and fixed this. Its a fuel pressure regulator, not easy to measure or put in.
    Then I found two of 4 tight exhaust valves, dealer used my shim measurements and his selection of spacer to set valves correctly.

    Between the two, mileage was back.

  4. #4
    Registered User
    Join Date
    Nov 2008
    Posts
    61
    Thank you so much for the inputs. There is no fuel leak for sure. But I will defiantly check my fuel pressure first. That's a very good point to start with. Let me find what's the pressure suppose to be and start from there.
    Thank you again.
    _____________
    Enjoy Riding and Ride Safe
    Sinclair & Mona Hamilton, NJ
    84 Honda Magna 500 / 85 BMW K100RS / K1200LT Will Be Next

  5. #5
    3 Red Bricks
    Join Date
    Jan 2007
    Location
    Pleasanton, Ca.
    Posts
    3,150
    Fuel pressure should be in the 37-40 range. With a failed regulator, it can get as high as 80-100. The easiest place to check it is to TEE in to the line that goes from the fuel rail to the regulator at the back end of the fuel rail. Make sure you TEE into it, as it still needs to be connected to the regulator.


    Another thing that fits your symptoms it a cracked crankcase vent hose (Beemer01 suggested this). It is a Zee shaped hose about 5/8" diameter and 6" long. It is located just to the rear of the cylinder head and to the inside of the throttle position switch on the rear end of the throttle bodies. The cracks will be right next to the top and bottom hose clamps. This hose vents the crankcase from the top of the block into the intake plenum. When this hose cracks (it always does), it allows unmetered air into the intake (large vacuum leak) and gives the symptoms you described. The hose is cheap $18 and can be changed easily. This would be my first check.


    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

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

  6. #6
    Benchwrenching PGlaves's Avatar
    Join Date
    Oct 2003
    Location
    "Big Bend" TX
    Posts
    8,497
    Internet diagnostics are risky, but remember that the "choke" is nothing more than a fast idle switch. I think you have a faulty engine temperature sensor causing a rich condition.
    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
    Registered User
    Join Date
    Nov 2008
    Posts
    61
    Thank all of you. I haven't check anything yet, but I will.
    I just did a long trip from New Jersey to Orlando 1140 mile within 19hrs as IBA requires 1000 miles/24hrs and came back yesterday. Now I'm sure my bike can only run under 150 mile with five gallons gas. For sure worse than before, I will work on it at this weekend. Started with checking vacuum hose leaking first. And then I might just replace the temp sensor.
    Paul, do you know how many temp sensors on this type bike? My bike doesn't have temp gauge on dashboard, so I assume it must be only one there. I thought it usually won't start if temp sensor fails. I might be wrong. I will keep it posted.
    _____________
    Enjoy Riding and Ride Safe
    Sinclair & Mona Hamilton, NJ
    84 Honda Magna 500 / 85 BMW K100RS / K1200LT Will Be Next

  8. #8
    Slipster Slipster's Avatar
    Join Date
    Jun 2012
    Location
    Broken Arrow, OK
    Posts
    72
    Did you install a new Z Hose? 98lee is correct in that it is the easiest and a logical place to start. Mine had very small cracks and the new hose corrected almost all of my rich mix issues.
    Expect The Unexpected

  9. #9
    Registered User
    Join Date
    Jun 2012
    Location
    Olympia, WA
    Posts
    158
    Check your valves, or have them checked and adjusted by a pro.
    Tim
    Olympia, WA
    1991 K75 - 121k Miles

  10. #10
    Registered User
    Join Date
    Jun 2003
    Location
    Northern Front Range, CO
    Posts
    6,323
    and not that it matters one bit to this issue... but there is no reason on the planet for changing your oil every 3K miles, unless you have a vested interest in keeping the oil companies in major profit mode. Every 6K is all that's called for, and manufacturers have a vested interest in recommending on the low side to begin with (gives them better liability protection in event of a breakdown issue).
    Ride Safe, Ride Lots

  11. #11
    Registered User rut3556's Avatar
    Join Date
    Apr 2012
    Location
    NH, USA
    Posts
    42
    >>but there is no reason on the planet for changing your oil every 3K miles,<<

    And this falls into the "to each his own" category.

  12. #12
    Registered User
    Join Date
    Jun 2003
    Location
    Northern Front Range, CO
    Posts
    6,323
    Quote Originally Posted by rut3556 View Post
    >>but there is no reason on the planet for changing your oil every 3K miles,<<

    And this falls into the "to each his own" category.
    always hoping to change behavior if it is based on old ideas or misinformation. if personal preference, for no particularly good reason, then yeah.. "to each his own."
    Ride Safe, Ride Lots

  13. #13
    Registered User
    Join Date
    Nov 2008
    Posts
    61
    I replaced the Z hose with new one less than two years. It still looks okay to me, but I didn't take it apart and get a close look. But is it possible that it will get rough idle if the hose leaking? It's snow here today. I have to wait until this weekend to check it again.
    Anyone knows what is average gas mileage on 85 k100RS?
    Thank all of you.
    _____________
    Enjoy Riding and Ride Safe
    Sinclair & Mona Hamilton, NJ
    84 Honda Magna 500 / 85 BMW K100RS / K1200LT Will Be Next

  14. #14
    3 Red Bricks
    Join Date
    Jan 2007
    Location
    Pleasanton, Ca.
    Posts
    3,150
    Quote Originally Posted by sinclairniu View Post
    But is it possible that it will get rough idle if the hose leaking?.
    Absolutely(that's why I suggested it)!

    Also, cracked vacuum caps on the throttle bodies will cause the problems you describe.

    You can't inspect your bike because it's snowing??? You shouldn't store your bike outside.



    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

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

  15. #15
    Registered User
    Join Date
    Jun 2003
    Location
    Northern Front Range, CO
    Posts
    6,323
    all Klassic Ks should get 40+ mpg, often 40+++. If you are below that you are either a) running quite hard at high rpms for extended jaunts, or b) doing only stop&go/stop&slow city type traffic, or c) something's wrong.
    Ride Safe, Ride Lots

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •