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Thread: 86 k100RT Rough Idle

  1. #1
    1986 K100RT, 135000 miles
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    Question 86 k100RT Rough Idle

    My K100RT has a rough idle, with a miss occasionally and also at about 2000 rpm which is about 35 mph it has a surge. I spoke to a old time BMW owner and he said the surging has been a problem with K bikes at about that RPM, anyone else expierence this. I changed the plugs but has not made a difference in the rough idle, seems more like a fuel problem to me. When you roll the throttle on everything is fine and no surging or misses at highway speed. This is my first BMW so I am still getting used toall of its actions.

  2. #2
    Registered User PHMARVIN's Avatar
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    Quote Originally Posted by pfetter View Post
    My K100RT has a rough idle, with a miss occasionally and also at about 2000 rpm which is about 35 mph it has a surge. I spoke to a old time BMW owner and he said the surging has been a problem with K bikes at about that RPM, anyone else expierence this. I changed the plugs but has not made a difference in the rough idle, seems more like a fuel problem to me. When you roll the throttle on everything is fine and no surging or misses at highway speed. This is my first BMW so I am still getting used toall of its actions.
    Hi. pfetter,
    I don't consider myself an "old time BMW owner", as I'm only 61 and have only owned 13 BMW bikes (7 airheads and 6 K-bikes) dating from 1977. I wouldn't know if my bikes surge (or have surged) at 2000 rpm, because I never run them at that rpm except when accelerating from a stop. 2000rpm in high gear is probably near 30mph on my K75's, and, if I'm at that speed, I'm probably in fourth or maybe third, not 2000 rpm in high gear. I would suggest if your bike does surge at 2000rpm in high gear, to not let it do so and downshift a gear or two. Don't spend any time or money trying to tune it out. You have more important things to do, like ride.
    Ride Safe,
    Phil Marvin - El Paso, TX
    '94 K75A/3
    '95 K75RTP

  3. #3
    3 Red Bricks
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    Like PH said, you shouldn't be running your bike at that low of an RPM except in first as you are accelerating away from a stop.

    I tell my wife, never run below 3000 RPM. If you do, you are lugging the engine. The power doesn't even START coming in 'till after 3000 RPM.

    Peak torque isn't until 6000 RPM on your engine and peak horsepower isn't until 8000 RPM. Redline is even higher.

    You need to get used to USING the RPM.

    As for the rough idle, could be a crack in one of the hoses or vacuum caps in the intake tract (most notably the crankcase vent hose) or could be tight exhaust valves (when was the last time the valve adjustment was checked?).

    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

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

  4. #4
    Registered User
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    Quote Originally Posted by pfetter View Post
    My K100RT has a rough idle, with a miss occasionally and also at about 2000 rpm which is about 35 mph it has a surge. I spoke to a old time BMW owner and he said the surging has been a problem with K bikes at about that RPM, anyone else expierence this. I changed the plugs but has not made a difference in the rough idle, seems more like a fuel problem to me. When you roll the throttle on everything is fine and no surging or misses at highway speed. This is my first BMW so I am still getting used toall of its actions.
    My 85K100RT does the same thing usually around 2300 -2500 RPM. Normal occurance is when riding in town and I don't like to have the engine reving at 3K plus. Have never noticed this on the open road since then the ole girl only see's 2500 RPM in first gear.

    It bothered be at first but now it is just part of the ride. When it fails to accelerate smoothly or starts giving problems at other RPM's then I will be concerned.

    Roy
    Roy G.
    85 K100RT Ol Ruby "Gone but not forgotten"

    02 K1200LTC Hoss

  5. #5
    1986 K100RT, 135000 miles
    Join Date
    Mar 2007
    Location
    Traverse City, MI
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    51
    Quote Originally Posted by PHMarvin View Post
    Hi. pfetter,
    I don't consider myself an "old time BMW owner", as I'm only 61 and have only owned 13 BMW bikes (7 airheads and 6 K-bikes) dating from 1977. I wouldn't know if my bikes surge (or have surged) at 2000 rpm, because I never run them at that rpm except when accelerating from a stop. 2000rpm in high gear is probably near 30mph on my K75's, and, if I'm at that speed, I'm probably in fourth or maybe third, not 2000 rpm in high gear. I would suggest if your bike does surge at 2000rpm in high gear, to not let it do so and downshift a gear or two. Don't spend any time or money trying to tune it out. You have more important things to do, like ride.
    Usually I will downshift to get the rpm's higher, I know it is the happiest at a higher rpm or actually about 70 mph. My major bother right now is the missing that I am experiencing at idle or pulling away in first gear, the bike used to idle right around 900 to 1000 rpm without much miss but now it will actually miss to the point where it might stall and then it will catch, this is just setting idling. I have not done anything except change plugs yet as I wasn't sure the direction to take at first. Thanks!!!!!!

  6. #6
    2-up and havin' fun sugarhillctd's Avatar
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    pfetter,

    First of all, it will help you and us if you put bike year (and model which you have already told us) in your signature- look at the bottom of other posts.

    And if possible post some history- whatever you know- about your RT. Total mileage plus any repair history- dealer or otherwise.

    There are several very experienced K bike owners here that will probably help you out if they know all the facts about your K100.

    Good luck,
    John
    John & Cathy
    '92 K100RS (gone- '04 R1100S Boxer Cup)
    '12 Suzuki DRZ400
    ("kid's" bikes) '02 Kaw ZX6R- Jen's '07 Duc 800ss- Johnnie's

  7. #7
    1986 K100RT, 135000 miles
    Join Date
    Mar 2007
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    Traverse City, MI
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    51
    Quote Originally Posted by SugarHillCTD View Post
    pfetter,

    First of all, it will help you and us if you put bike year (and model which you have already told us) in your signature- look at the bottom of other posts.

    And if possible post some history- whatever you know- about your RT. Total mileage plus any repair history- dealer or otherwise.

    There are several very experienced K bike owners here that will probably help you out if they know all the facts about your K100.

    Good luck,
    John
    Thanks for the heads up, will take care of it as soon as I get time..

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