K11 Owners Group

Grunter · Posted: Fri May 07, 2021 2:47 am Post subject: Bike will not rev over 5500

I am trying to find the cause of a problem a friend of minis having with his 1986 K75s (Yes I know it is not a K1100 but we are really struggling here).

He has a problem where the motor will not rev over 5500rpm, in any gear and at any speed, even on the stand.

It runs perfectly until the engine reaches that critical speed when it feels as if the rev limiter is cutting in early. On a K75 this should be around 9000rpm

So far:-

He has been right through the fuel pipes and changed them all, both inside and outside of the tank. Pressure regulator functioning perfectly

New fuel filter, exchanged the fuel pump for a known good one.

Swapped the Hall sensor for a known good one, checked and cleaned the cable to the ignition trigger.

Swapped the ignition leads from his other K75s

Swapped the coils from his other K75s

Low tension leads to the coils cleaned and refitted

New plugs which are correctly gapped and the right colour/type

Apart from that he is stuck for ideas.

I have been thinking, is it possible that the air flow meter is not opening correctly, possibly due to ingress of dirt of some sort. It is a bit of a fiddle to remove to check, so thought I would ask other opinions before I mentioned it to him.
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1997 K1100LT
1994 R1100RS

flybd5 · Posted: Fri May 07, 2021 2:49 pm Post subject:

I assume you checked to make sure the injectors and plugs are getting a good signal?

If so, maybe clogged fuel injectors? See post #14 here: https://www.k100-forum.com/t1590-won-t-rev-past-5000
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To err once is human. To do so repeatedly is incompetence.
1995 K1100LT SE

Grunter · Posted: Fri May 07, 2021 3:43 pm Post subject:

Yes the owner has done this. Up to 5500rpm the bike runs perfectly which most probably would not because of an injector fault.

The latest suspect is a lack of signal between the air flow meter and the injector control. Around 2/3rds throttle the air flow meter is supposed to send a signal to the injector control to enrich the mixture

This is supported because when he rolls off the throttle there is a small power surge. There is a paragraph on page 227 of the Clymer Manual from 1991 which point this out.

Going by this it may be either the signal is not being sent, or if it is the injector control unit is faulty and not receiving it or not recognising it. So in effect with no signal = a weak mixture and the refusal to rev any faster.
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1997 K1100LT
1994 R1100RS

flybd5 · Posted: Fri May 07, 2021 4:01 pm Post subject:

Grunter · Posted: Fri May 07, 2021 4:23 pm Post subject:

A K75 only has 3 cylinders not 4
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1997 K1100LT
1994 R1100RS

flybd5 · Posted: Fri May 07, 2021 5:04 pm Post subject:

I think the point is that the symptom *can* be caused by faulty injector(s)...
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To err once is human. To do so repeatedly is incompetence.
1995 K1100LT SE

Grunter · Posted: Fri May 07, 2021 6:05 pm Post subject:

I had already said he had checked the injectors, 3rd post down.
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1997 K1100LT
1994 R1100RS

flybd5 · Posted: Fri May 07, 2021 7:19 pm Post subject:

No, you answered my question as to whether the injectors and plugs were getting a good signal.
_________________
To err once is human. To do so repeatedly is incompetence.
1995 K1100LT SE

Flying Duck · Posted: Fri May 07, 2021 9:30 pm Post subject:

If you suspect that the engine is running too lean then hit the start button and see what impact that has. It enriches the mixture if the bike is running.

I don't know if K11 Motronics do this too but the L-Jetronics on 2V Ks do.
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93 LT (x2)
94 RS
86-97 K75F(K75/100/1100 Frankenbrick)
86 K75C w/paralever, hi perf cams,TURBO!
91 & 92 K75Ss
91 K1
86 custom K100
14 WR250R
IBA #17739 (SS1K, BBG, 50CC)
Buy parts HERE

Grunter · Posted: Sat May 08, 2021 2:38 am Post subject:

I feel that I may not have explained it properly.

The bike is NOT running lean.

The fuel air mixture changes the wider open the throttle is so around 2/3rds throttle or in the case of the guy I am trying to help, when the bike is running at speed under load, in other words about 5500rpm, there is an electronic signal sent from the air flow meter to enrich the mixture but in this case does not seem to be happening. Hence the reason it will not accelerate past 5500rpm when under load.

It is a more advanced method of carburation where, with old 2 valve air cooled boxers, about the same time (about 2/3ds throttle) The fuel coming from the pilot jet is insufficient and the needle valve allows the main jet to take over and provide more fuel, only with the injection on both the K100 and K75,this is done electronically
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1997 K1100LT
1994 R1100RS

Flying Duck · Posted: Sat May 08, 2021 1:38 pm Post subject:

If you suspect it's a MAF sensor issue then try swapping those. It's not really that hard to do.

http://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/maf/maf.htm
_________________
93 LT (x2)
94 RS
86-97 K75F(K75/100/1100 Frankenbrick)
86 K75C w/paralever, hi perf cams,TURBO!
91 & 92 K75Ss
91 K1
86 custom K100
14 WR250R
IBA #17739 (SS1K, BBG, 50CC)
Buy parts HERE

Grunter · Posted: Sun May 09, 2021 5:44 am Post subject: Problem Solved

He removed the airflow meter from the bike an opened it up. Someone before his ownership of the bike had butchered it! Whatever was done which is not altogether clear but it had been put back together and sealed with silicon sealer. One bit of sealer had dropped onto a gear wheel and stopped full movement of the butterfly flap a suggested earlier.

The UK firm of Motorworks who dismantles BMW's have sold him a working used one for £95 and comes with a 6 month warranty.

I have a picture, but there does not seem to be a facility to upload it.
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1986 K75S Professionally resprayed in Nightfire Metallic Red (non BMW colour) and refurbished wheels.

1986 K75c. Good mechanical order. Now resprayed BMW Avus Black (unlined) and looking good.
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1997 K1100LT
1994 R1100RS

Flying Duck · Posted: Sun May 09, 2021 10:05 am Post subject:

Glad to hear that you've found the issue.

The K11OG site does not host images. Yon need to upload it elsewhere. I use IMGUR these days. It's 100% free and you don't even need to set up an account to use it.

https://imgur.com/upload
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93 LT (x2)
94 RS
86-97 K75F(K75/100/1100 Frankenbrick)
86 K75C w/paralever, hi perf cams,TURBO!
91 & 92 K75Ss
91 K1
86 custom K100
14 WR250R
IBA #17739 (SS1K, BBG, 50CC)
Buy parts HERE

Grunter · Posted: Sun May 09, 2021 12:21 pm Post subject:

Sorry I don't use 3rd party hosting. That for me seems a little bit longwinded
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1997 K1100LT
1994 R1100RS

Jim · Posted: Sun May 09, 2021 9:38 pm Post subject:

Good to know you got it sorted!

I think the newer versions of php allow direct uploads - not sure. But, since the owner of this forum has never charged us anything, we probably can't complain too much.
_________________
Jim
1997 K1100LTSE 94,000 - has gremlins!
1995 R100RT Classic 16,650 crashed - repairing
1992 K75RTP 46,000
1992 R100R 24,000 - FOR SALE

"We shall not all die, but we shall all be changed."

Grunter · Posted: Mon May 10, 2021 7:24 am Post subject:

I know of at least one MC forum in UK that uses the same software as this one and there is the facility for direct uploads.
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1997 K1100LT
1994 R1100RS

Scott_Anderson · Posted: Mon May 10, 2021 4:53 pm Post subject:

Jim can correct me if I'm wrong on this but the picture issue is more of who pays for the storage space all the pictures take up.

Pretty much why Photbucket quit hosting photos for FREE, took up too much server storage space and it was costing them too much.
With cameras and smartphones taking higher quality pictures, file sizes are growing exponentially, to that end some sites are starting to limit upload image quality(ie file size) to keep storage space in check.

The owner here has been very gracious and has not been charging any fees(nor asking for donations) what so ever to host this forum as it is for almost 20+ years, yet still paying the hosting fees out of his pocket.
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Ride safe.

1995 K1100LT 0302044
1997 R1100RT ZC62149
2017 FLHTK Ultra Limited
Garmin StreetPilot 2820
Garmin Zumo 550
Garmin Zumo XT
"One who does not ask questions is ashamed to learn" Danish proverb
1997 K1100LT 0302488(R.I.P.)

Flying Duck · Posted: Mon May 10, 2021 6:09 pm Post subject:

SugarHillCTD · Posted: Tue May 11, 2021 7:02 am Post subject:

Yeah, I got caught in the pay for hosting picture routine.

Flickr limits their free hosting to 1000. Some of my older posts here in Tech no longer have images because of that. Crying or Very sad

_________________
John & Cathy

'92 K100RS4V Pearl White SOLD
'04 K1200GT
IBA Several-SS1k, BBG, 50CC NYC to S.F.

Grunter · Posted: Tue May 11, 2021 12:07 pm Post subject: Uploading pictures

No problem really but as they say a picture is worth a thousand words and if it were to help it would have been better.
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1997 K1100LT
1994 R1100RS