BMW K bikes (Bricks)


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1Back to top Go down   Poor idle Empty Poor idle Wed May 22, 2024 6:04 pm

slowandlow

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Hey there!

My K100 RS- 85 is having trouble at low rpm and low power load.

The idle is somewhat uneven, but worse, the engine suddenly misses out, its hacking for a fraction of a second, looses momentum and then quickly returns to pace. As if you would chop the idle with an axe, or cutting it with scissors.

This can happen fx every five or ten second, or other times only every minute or so. At speeds above ca 50 kmh and at high power loads the engine runs completely perfect.

I've done fuel tank restauration, new fuel hoses, new ignition cables, new plugs.

Has anyone experienced similar issues? Could a faulty Hall- transmitter cause this problems? Or dirty injektion nozzles?

Grateful for any tips! 🙂

Brg/ Örjan.

    

2Back to top Go down   Poor idle Empty Re: Poor idle Wed May 22, 2024 9:31 pm

Laitch

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Have you directed a narrow spray of volatile carburetor cleaner, propane, Mapp gas, or acetylene around the z-hose connection from the crankcase to the plenum, each throttle body's air intake hose from the plenum, and each throttle body's intake manifold connection at the cylinder head to determine if doing that raises the idle? There could be deterioration causing air leaks at one or more of those points fouling the air:fuel mixture.


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1995 K75 90,000 miles
    

3Back to top Go down   Poor idle Empty Re: Poor idle Wed May 22, 2024 10:10 pm

duck

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Sounds symptomatic of cracks/leaks in the boots between the throttle bodies and the cylinder head.

They will leak at idle and then when the vacuum increases at higher RPMs the vacuum kind of seals them.

Part 11611460408

As Laitch suggests spraying some unlit propane from a torch around them at idle is a good way to diagnose.


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Current stable:
86 Custom K100 (standard fairing, K75 Belly pan, Ceramic chromed engine covers, paralever)
K75 Frankenbrick (Paralever, K11 front end, hybrid ABS, K1100RS fairing, radial tires)
86 K75C Turbo w/ paralever
94 K1100RS
93 K1100LT
91 K1
93 K75S (K11 front end)
91 K75S (K1 front end)
14 Yamaha WR250R
98 Taxi Cab K1200RS
14 K1600GT
http://www.ClassicKBikes.com
    

4Back to top Go down   Poor idle Empty Re: Poor idle Thu May 23, 2024 3:03 am

slowandlow

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Hi, thanx for reply, ill try the gas- test, however, since the engine running at idle is kind of "chopped up" very briefly, does that really point at air/ fuel problems, or rather ignition issues? Ive read in my Clymer that the engine indeed works with different ignition programs at different rpms, hence my question. 🙂
Thanx!

    

5Back to top Go down   Poor idle Empty Re: Poor idle Thu May 23, 2024 8:33 am

92KK 84WW Olaf

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Check Z pipe, check if you have a vacuum pipe from no 1 throttle body, early 85 Ks have one, replace it with a vacuum cap.

Balance throttle bodies too, but also check the throttle position sensor [TPS]. My 84 RT did what yours is doing and that cured it.

Early Ks suffer coil and HT lead failure too. BSK Speedworks sell a replacement coil and HT lead package that is very good value.


__________________________________________________
1992 K100LT 0193214 Bertha Blue 101,000 miles
1984 K100RT 0022575 Brutus Baja Red 578 bought 36,000 now 89,150 miles
1997 K1100LT 0188024 Wotan Mystic Red 689 58,645 now 106,950 miles Deceased.
1983 K100RS 0011157 Fricka 606 Alaska Blue 29,495 miles Damn K Pox Its a Bat outta Hell Now 58,200 miles. 
1996 K1100LT 0233004 Lohengrin Mystic Red 38,000 miles currently 49,200 miles.
1983 K100RS 0004449 Odette R100 colours 58,000 miles. Sprint fairing now 63,390 miles

Past:
1968 Yamaha 80 YG1
1971 Yamaha 125 YAS-1
1968 Honda 125 SS
1970 Honda CD 175
1973 Honda CB500-4
Honda CX 500
    

6Back to top Go down   Poor idle Empty Re: Poor idle Thu May 23, 2024 12:09 pm

slowandlow

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Z- pipe is ok. What is "HT lead" ? 🙂

    

7Back to top Go down   Poor idle Empty Re: Poor idle Thu May 23, 2024 12:29 pm

Bricklayer

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American English it is "Spark plug wires".

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8Back to top Go down   Poor idle Empty Re: Poor idle Thu May 23, 2024 1:35 pm

Laitch

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slowandlow wrote:. , , does that really point at air/ fuel problems, or rather ignition issues?
Maybe you should just go where your heart leads you. Poor idle 112350


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1995 K75 90,000 miles
    

9Back to top Go down   Poor idle Empty Re: Poor idle Thu May 23, 2024 2:25 pm

Point-Seven-five

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The air/fuel ratio is most sensitive to leaks at small throttle openings like occur at idle and in low speed/light load situations .  These leaks can lean out the mixture to where it won't reliably ignite in the cylinder.  As the throttle opening is increased at higher rpm/loads, this small amount of unmeasured air that is leaking affects the overall mixture much less so engine operation improves. 

Also, at heavier loads and higher rpm with the throttle wider, the manifold vacuum is less so there is less suction to pull unmeasured air through the leaks into the intake manifold.


__________________________________________________
Present: 1991 K100RS "Moby Brick Too"
 
Past:
1994 K75RT "Ilsa, She Wolf of the SS"
1988 K100RS SE "Special Ed"
1994 K75S "Cheetos"
1992 K100RS "Moby Brick" R.I.P.
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

10Back to top Go down   Poor idle Empty Re: Poor idle Thu May 23, 2024 3:38 pm

slowandlow

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Aha, ignition cables? 🙂 Have replaced them with a german made package, still got the problems. I will check the coils and see if i can measure them to get wiser.

    

11Back to top Go down   Poor idle Empty Re: Poor idle Thu May 23, 2024 3:42 pm

firstle

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battery low

    

12Back to top Go down   Poor idle Empty Re: Poor idle Thu May 23, 2024 4:46 pm

slowandlow

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Nope, new battery: 13,4 Volt at idle, 13,8 volt at higher rpm. 🙂 How does the Hall- transmitter work? Can it be mechanically worn out, or does it either work or doesn't work at all?

    

13Back to top Go down   Poor idle Empty Re: Poor idle Thu May 23, 2024 7:13 pm

Laitch

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slowandlow wrote:How does the Hall- transmitter work? Can it be mechanically worn out, or does it either work or doesn't work at all?
Your Brick has two Hall Effect Sensors. If one of them failed, you would be unlikely to characterize the performance of the engine as "runs completely perfect" no matter the speed. "Completely perfect" would also be an elusive condition with a bad coil.



Last edited by Laitch on Thu May 23, 2024 7:27 pm; edited 1 time in total


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1995 K75 90,000 miles
    

14Back to top Go down   Poor idle Empty Re: Poor idle Thu May 23, 2024 7:24 pm

Jordan53

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slowandlow wrote:Nope, new battery: 13,4 Volt at idle, 13,8 volt at higher rpm. 🙂 How does the Hall- transmitter work? Can it be mechanically worn out, or does it either work or doesn't work at all?
A Hall Effect device outputs a square wave. It switches ON or OFF, according to whether a magnetic field is sensed.
It is more likely to work properly or fail completely, rather than partially work.


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1989 K100 RS

VIN: xxx0149621
    

15Back to top Go down   Poor idle Empty Re: Poor idle Fri May 24, 2024 4:37 am

slowandlow

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Where is the other Hall sensor? Ive also been told it could be the throttle position switch (next to the no 4 intake) since a bad switch could influence the engine performance. And also, a bad connector down at the coolant temperature sensor cold disturb engine/ ignition, since this sensor- when connector completely removed/ pulled out- will shut down the engine as an overheating protection action. Anyone having opinions to that?

    

16Back to top Go down   Poor idle Empty Re: Poor idle Fri May 24, 2024 12:44 pm

Laitch

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slowandlow wrote:Ive also been told . . .
Anyone having opinions to that?
I'm glad you asked!

Orderly system testing beats random theorizing any day. Could a faulty coolant temperature sensor be involved in this? Yes. So could intake air leaks, karmic debt or ancestral curses.

Hall Sensor II is 180º from Hall Sensor I on the same plate. Here's a link to a post that also contains a link to a downloadable pdf of the BMW LE Jetronic Manual that explains how your Brick's engine is managed. It could put things in perspective.

Testing guidance is also available on the Tech Page here in the form of illustrated documents titled Electronic Troubleshooting The EFI and Testing The Hall Sensors.


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1995 K75 90,000 miles
    

17Back to top Go down   Poor idle Empty Re: Poor idle Fri May 24, 2024 1:18 pm

slowandlow

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Excellent, thanx! 🙂👍

    

18Back to top Go down   Poor idle Empty Re: Poor idle Fri May 24, 2024 2:34 pm

Two Wheels Better

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slowandlow wrote:...I've also been told it could be the throttle position switch (next to the no 4 intake) since a bad switch could influence the engine performance....
For easier reference for forum members who may have advice, consider going to the Profile section of the forum and under Signature, add the year & model (& even the last 7 digits of your VIN) to your posts every time.

The TPS is simply an on/off switch on LE Jetronic K bikes like yours, unlike the later Motronic (16V) K100 & K1100 models where it's a sensor. Some folk get about with the thing unplugged for less abrupt throttle feel. They have a very low failure rate, but unplug it and see if the symptom persists.


__________________________________________________
1977 R75/7-100, '93 K11/K12 Big Block, '93 K1100RS, '95 R100 Mystic, '96 K1100RS, 2 x '98 K1200RS, '06 K1200R & '09 K1300GT. Projects: 1993 & '96 K1100RS, & the 2nd '98 K1200RS
    

19Back to top Go down   Poor idle Empty Re: Poor idle Fri May 24, 2024 2:54 pm

Laitch

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Two Wheels Better wrote:The TPS is simply an on/off switch on LE Jetronic K bikes like yours, . . . unplug it and see if the symptom persists.
A good suggestion, and success would pretty much eliminate ancestral curse as an underlying condition.



Last edited by Laitch on Fri May 24, 2024 7:05 pm; edited 1 time in total (Reason for editing : Clarity for posterity.)


__________________________________________________
1995 K75 90,000 miles
    

20Back to top Go down   Poor idle Empty Re: Poor idle Sun May 26, 2024 3:56 am

slowandlow

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BTW, when engine is running, if i press the start button the rpm is rising, when i let go the rpm returns down to idle. Is this normal (electrical controlled "choke" at start sequence), or is my start button broken?

    

21Back to top Go down   Poor idle Empty Re: Poor idle Sun May 26, 2024 8:22 am

Two Wheels Better

Two Wheels Better
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slowandlow wrote:BTW, when engine is running, if i press the start button the rpm is rising, when i let go the rpm returns down to idle. Is this normal (electrical controlled "choke" at start sequence), or is my start button broken?
Think of it as a hidden booster rocket.


__________________________________________________
1977 R75/7-100, '93 K11/K12 Big Block, '93 K1100RS, '95 R100 Mystic, '96 K1100RS, 2 x '98 K1200RS, '06 K1200R & '09 K1300GT. Projects: 1993 & '96 K1100RS, & the 2nd '98 K1200RS
    

22Back to top Go down   Poor idle Empty Re: Poor idle Sun May 26, 2024 8:49 am

firstle

firstle
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BTW, when engine is running, if i press the start button .......... really ? can this be done without damage to the motor 

    

23Back to top Go down   Poor idle Empty Re: Poor idle Sun May 26, 2024 8:54 am

Two Wheels Better

Two Wheels Better
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It's not recommended as a habit but it richens slightly the mixture.


__________________________________________________
1977 R75/7-100, '93 K11/K12 Big Block, '93 K1100RS, '95 R100 Mystic, '96 K1100RS, 2 x '98 K1200RS, '06 K1200R & '09 K1300GT. Projects: 1993 & '96 K1100RS, & the 2nd '98 K1200RS
    

24Back to top Go down   Poor idle Empty Re: Poor idle Sun May 26, 2024 9:39 am

Laitch

Laitch
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firstle wrote:really ? can this be done without damage to the motor 
If a corporate reference would help, here's a slightly fuzzy extract from p.16 of BMW's LE Jetronic training manual.
Poor idle Screen47


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1995 K75 90,000 miles
    

25Back to top Go down   Poor idle Empty Re: Poor idle Sun May 26, 2024 10:10 am

Point-Seven-five

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If engine speed increases when you press the start button it indicates that the idle mixture is lean.  This is normally caused by air leaks downstream of the air flow sensor. Although you seem to be fixated on ignition/electrical issues, I, personally, would spend my time investigating air leaks.


__________________________________________________
Present: 1991 K100RS "Moby Brick Too"
 
Past:
1994 K75RT "Ilsa, She Wolf of the SS"
1988 K100RS SE "Special Ed"
1994 K75S "Cheetos"
1992 K100RS "Moby Brick" R.I.P.
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

26Back to top Go down   Poor idle Empty Re: Poor idle Sun May 26, 2024 12:09 pm

firstle

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500rpm ? i must adjust the tick over on my k100

    

27Back to top Go down   Poor idle Empty Re: Poor idle Sun May 26, 2024 12:13 pm

Laitch

Laitch
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Intermission.
Poor idle Edison11



Last edited by Laitch on Sun May 26, 2024 6:07 pm; edited 1 time in total (Reason for editing : Replacing futility with history.)


__________________________________________________
1995 K75 90,000 miles
    

28Back to top Go down   Poor idle Empty Re: Poor idle Mon May 27, 2024 4:18 am

slowandlow

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Thanx, ill continue my investigations... 🙂

    

29Back to top Go down   Poor idle Empty Re: Poor idle Fri Jun 07, 2024 4:27 am

slowandlow

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Well that was easy, i did the gas can spray test and sure enough, i got a nice rise of the idle... 🙂 It looks like all 4 upper and lower rubber tubes/ manifolds are bad... 🙁 Ill also check those connectors for wear and tear. BTW, how do i remove the connector on the Throttle position switch? It has a metal clip around, do i just pull upwards until it releases or should the clip first be removed? Thanx!

    

30Back to top Go down   Poor idle Empty Re: Poor idle Fri Jun 07, 2024 5:58 am

Dai

Dai
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You can try just pulling it off, but it may resist. In this case 'carefully does it'  because you do NOT want to lose/break that clip. Look at it carefully - both short sides fit into a shallow slot. Use a small screwdriver (a so-called 'jeweller's screwdriver') to lever out the side nearest to you. As you lever it out, the clip will start to rotate so make sure your other hand is in a position to stop it from pinging off. You only need one side out before you should be able to remove the TPS housing. As soon as the housing is off, push the clip back into the slot. The housing will push back on with the clip in place.

If you ever need to remove the housings from the fuel injectors or the thermostat housing (behind the radiator), use the same procedure.

If you do lose the clip, new ones are available from any specialist electronics shop or ebay. Ask for a clip for a 'three-way junior timer housing'. For the fuel injectors, they are a 'two-way junior timer housing'.

If the manifold and inlet rubbers are toast, you will also need to replace the crankcase breather, the vacuum caps and the vacuum tube on no.4 cylinder. Talk to Motorworks about secondhand manifold and inlet rubbers, but buy new vacuum caps, vacuum tube and crankcase breather.

When refitting the manifold and inlet rubbers, you have two choices. You can either buy new oetiker clamps and the tool to fit them, or go for 8mm-wide worm drives (which is what most of us have done - again, talk to Motorworks). If you use worm drives then buy stainless steel ones because you don't want to find that you need to remove the throttle bodies in future and discover that the worm drives have rusted solid. Be VERY careful when positioning the worm drives for cylinders 2 and 3 as it is very easy to foul the throttle bodies and jam the throttle open (or have it not open at all).


__________________________________________________
1983 K100 naked upgraded to K100LT spec after spending time as an RS and an RT
1987 K100RT
Others...
1978 Moto Guzzi 850-T3, 1979 Moto Guzzi 850-T3 California,1993 Moto Guzzi 1100ie California
2020 Royal Enfield Bullet 500
    

31Back to top Go down   Poor idle Empty Re: Poor idle Fri Jun 07, 2024 11:17 am

slowandlow

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Great, thanx alot! 🙂👍 ( I can remove only the connector (without removing the TPS housing) just to check the pins, right?)

    

32Back to top Go down   Poor idle Empty Re: Poor idle Sat Jun 08, 2024 5:38 am

Dai

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Yes.


__________________________________________________
1983 K100 naked upgraded to K100LT spec after spending time as an RS and an RT
1987 K100RT
Others...
1978 Moto Guzzi 850-T3, 1979 Moto Guzzi 850-T3 California,1993 Moto Guzzi 1100ie California
2020 Royal Enfield Bullet 500
    

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