Bought this bike a few weeks ago for cheap, figuring I could sort it out over the winter and have a solid RS, if not perfect, cosmetically. Here's what I brought home.


I've been struggling to get this one running, picking brains over at the MotoBrick, making mistakes and generally scratching my head trying to revive the bike. Meanwhile, I've been piecing it together using the parts that came with the bike, and sourcing the missing pieces.


The more I look, the rattier this bike is. Although the PO has owned it since '87, It doesn't appear to have been well kept. Paint work is scruffy at best, broken off mounting tabs on body work, discoloration on alloy parts, and rusty frame. The lowest pipe on the Luftmeister exhaust has pinholes. I'm beginning to think even at the bargain price, I paid too much. 

But then again, I might just be hitting a low point in the renovation cycle. If I could just get it running decently it would be encouraging.

It doesn't look too bad in the pic's Swampy , reverse the ugly mod's ( mirror pods etc ) , give everything a bit of TLC and you will have a nice machine

John Re

Melbourne Australia

JR_K100RS wrote:It doesn't look too bad in the pic's Swampy , reverse the ugly mod's ( mirror pods etc ) , give everything a bit of TLC and you will have a nice machine

John Re

Melbourne Australia

Thanx! Not too much going on with the project due to demands of the holiday season, but I have sourced all the fairing inner panels and some fixings. I also sourced some RS handlebars to replace the S bars. If they prove to be too cramped I can always swap back but I thought I'd like to bring this bike back to box-stock and make my own mods if necessary. 
As it stands, I still don't have the engine running properly. It's getting plenty of fuel. I replaced the injectors thinking they may be crudded up from sitting and trying to pass the bad fuel/water that was in the tank. But spark looks weak and jumps from electrode to the threaded body of the plug, and when I did have it running it was on 3 cylinders (if I wanted a 3 cylinder bike I would've bought a K75, dammit!).
As John says, it would be nice to restore the original mirrors, even though they are a bit narrow spaced, although I understand why someone might ditch them for 'bar-mounted ones. I had the same problem with my R100RS where I was looking at my elbows half the time. The P.O. said he had the mounts faired over during some body work to repair the fairing after a drop.
The body work is a bit scruffy, so a decent paintjob and maybe a replacement upper fairing piece would do the bike some good. The priority right now is to have a decent running and mechanically sorted bike by spring. Cosmetic renovations can follow.

About the mirrors/turn signals.  I have a friend who when he had his RS got tired of replacing the glass that kept falling out of the mirrors as well as the pods that seemed to fall off if you looked at them. 

He bought some LED signals and bar mount mirrors, faired the old mounting points on the fairing.  The bike looked so much better without those huge pods hanging off the side of the fairing!  It didn't look as dated as it did with the pods.  Even the flat windscreen and the square headlight look less "vintage". 

The only downside, if you want to call it that, is that the wind on your knuckles is no longer deflected away from them.  I suspect they add to the high speed drag as the K1 doesn't have those ugly pods.

Back on the RS Reno project after the holidays. I swapped out the C 'bars for a set of RS 'bars, along with replacing the throttle cable (don't ask why!). In doing so I overtightened the pinch bolt on the clutch side control and broke the threaded tab !@#$%. After threading the replacement cable in I found that there is way too much slack in it. Looks like I'll have to make up a spacer down at the throttle body end. 
Putting the airbox back in place, one of two remaining the spring clips just disintregrated. !@#$%

And I still haven't gotten the thing running properly.

swampyankee wrote: After threading the replacement cable in I found that there is way too much slack in it. Looks like I'll have to make up a spacer down at the throttle body end.

That is a classic problem encountered with some aftermarket cables. What's the total length of the cable from barrel end to barrel end? Can you post a photo or a link to what you purchased?

Back from vacation and ready to continue tinkering. I bought some airbox clips and a clutch-side control base from a guy on FB Marketplace. Hopefully I can install it without snapping it off at the punch bolt like I did the last one D'OH!!)

And to work on that cable. I'll have to pull it to measure outer and inner length. I bought the cable on eBay and assumed it was OEM, but maybe not. Any idea how much the inner is supposed to stick out if the slack is pulled to one end? I'll need to turn up a spacer bushing for it.

You should be able to see a part number printed on the clutch cable along with the letters "BMW".  This will tell you it's a factory cable and make it possible to check the length.

Look at the last three digits of the part number on the cable.  They should be either 955 or 960.  The 955 is 1510MM long and the 960 is 1625MM long

The long 960 cable is used on the RT and LT bikes with the high handle bars while the 955 is used on the C, S and RS models that have low bars.

I fished the cable out and measured free length at about 4". The pic shows it end in what looks like 9 06 92 FHP. Not sure how that relates to the numbers you listed. Bottom line is I'm going to have to make a spacer.

swampyankee wrote:I bought the cable on eBay and assumed it was OEM, but maybe not.

FYI: OEM cables have the BMW part number printed on them.

Is that the only number on the cable?  9 06 92 looks to me like a manufacture date.  September 6 1992, or possibly 9 June 1992.  FHP looks like it might be an aftermarket parts manufacturer. 

Is there a 6- 7 digit or longer number printed on the cable anywhere with BMW printed in line with it?  As I mentioned above, there are three digits at the end of that number that will identify the length.  The official part number might be printed without spaces 2324XXX or as the parts list shows it 2-324-XXX.  The X's will be either 955 or 960.

If the printed number is longer than 6 or 7 digits it should start with either 32-73 or 32-73-2.

My apologies. I tried to insert the pic I took while in the garage last night and it didn't take. I've since edited my post above to show the pic.
The sequence starts with "BMW" so I assume its an OE item. The problem is with the inner cable having too much slack. It appears to have about 1" more slack than the cable I removed. I've sketched up a spacer bushing using the plastic bushing I snipped off the old cable. I'm hoping to turn up one out of nylon in the next couple days. Any caveats?

Instead of using plastic for machining a spacer (Post 12) you could use brass. I used brass when I made up a custom throttle cable. Brass is strong, easy to machine, essentially is non-corrosive and can cope with high temperatures.

This is what is in your photograph, swampyankee. It was used from 06/86



This is the low bar RS  cable used pre-06/86

Doh!  I read that you mentioned clutch in the post so I thought you were talking about the clutch cable. 

Disregard what this dumb f*ck posted.

Laitch wrote:This is what is in your photograph, swampyankee. It was used from 06/86



This is the low bar RS  cable used pre-06/86

Where can I find closer-up pics of these? I can't quite read the measurements shown and it would be quite helpful. As near as I can tell, the "free length" looks to be the same as the one I have - 4" total. If so, maybe I have it intsalled incorrectly??

I use MaxBMW's parts fiche for parts information and comparison. Clicking on any photo images in it enlarges them. You'll find these and other images in the Steering category of the K100RS 2V Model section of the fiche.

Here's the large print edition.

Before 06/86


From 06/86

The free length looks to be about the same as the cable I have. However, the one I pulled out measured about 1" shorter. 

BTW, when I said plastic, it'll probably be delrin or something similar - whatever I can find out in the shop.

swampyankee wrote:The free length looks to be about the same as the cable I have.

We've gone apples and crabapples. We're looking at two different ends. The photo in my previous post of the Before '86 end is the end that attaches to the throttle body. The photo of the From '86 end is the end that attaches to the handlebar throttle gear assembly.


Here's the From '86 end that attaches to the throttle body, where you seem to be involved.

Laitch wrote:

swampyankee wrote:The free length looks to be about the same as the cable I have.

We've gone apples and crabapples. We're looking at two different ends. The photo in my previous post of the Before '86 end is the end that attaches to the throttle body. The photo of the From '86 end is the end that attaches to the handlebar throttle gear assembly.


Here's the From '86 end that attaches to the throttle body, where you seem to be involved.

Understood. I was looking at both ends to determine a total free length, which could be about 4" like mine. Since my bike production date is 11-13-1985, I wonder if it's early-year enough to be the before-86 version even though it's an '86 model year. What may be a clue is that my original cable has a black plastic bushing ion the throttle-body end, whereas my "new" one has white plastic. The colors are the same in the Max BMW pics for early and later year.

swampyankee wrote: .  . . my bike production date is 11-13-1985 . . ..

If that is the manufacturing date then it is in the before 06/86 category.

You have the correct cable for your bike.  Something else is missing or incorrect and you need to figure out what it is.  First thing I would suggest is that you put the last seven digits of the VIN in the box at RealOEM.  Then you will have the parts list used to build YOUR bike.  Then you can check what you have against what you need to get things the way they should be.

RealOEM

You bike was originally made with a different throttle cable that was discontinued around 1986 and replaced with what you have now.  There are a couple additional parts that are needed to make the whole thing work, and I suspect that one of them is missing.  The RealOEM list will help identify exactly what you need to make it work properly. 

I suggest this because control functions like the throttle on a machine with almost 100hp can cause embarrassing, expensive, or even dangerous problems like over revving so I would recommend using the right parts.

Point-Seven-five wrote:You have the correct cable for your bike.  Something else is missing or incorrect and you need to figure out what it is.  First thing I would suggest is that you put the last seven digits of the VIN in the box at RealOEM.  Then you will have the parts list used to build YOUR bike.  Then you can check what you have against what you need to get things the way they should be.

RealOEM

You bike was originally made with a different throttle cable that was discontinued around 1986 and replaced with what you have now.  There are a couple additional parts that are needed to make the whole thing work, and I suspect that one of them is missing.  The RealOEM list will help identify exactly what you need to make it work properly. 

I suggest this because control functions like the throttle on a machine with almost 100hp can cause embarrassing, expensive, or even dangerous problems like over revving so I would recommend using the right parts.

Thanx for the link.

Obviously, the throttle cable I pulled out is the original superseded version. What I'm missing is whatever parts they used to retrofit the newer style cable as a replacement for the earlier one. I see a bushing in the diagram but no explanation of what it, whether it's used to retrofit, or how it's installed.... Back to the drawing board.

Can you post the last 7 digits of your VIN?  It will make it possible for us to research what you have and how it works.

swampyankee wrote:What I'm missing is whatever parts they used to retrofit the newer style cable as a replacement for the earlier one. I see a bushing in the diagram but no explanation of what it, whether it's used to retrofit, or how it's installed.... Back to the drawing board.

Here's a photo of the bushing, the adjusting screw and the nut on the adjusting screw. The bushing is slid into the handlebar throttle assembly, the throttle cable is pushed into the adjusting screw and the bare cable end gets connected to the throttle chain. If your original cable did not have this assembly then it's likely the pre-06/86 throttle cable. Here's how Rick G describes it.

JEEZUM CROW! Snowmaggedon is here right now!

Laitch wrote:JEEZUM CROW! Snowmaggedon is here right now!  

It's a winter wonderland!

Looks to be about a foot of global warming so far.

FWIW, here's the report I got when I entered my VIN into the decoder:


http://forum.kforum-tech.com/members-upload/uploads/BMW_K58_K100_1985_avus-schwarz,_Zierl_--_--_-_-_WB1051306G0043204.pdf


I do have the adjuster at the handlebars as described and I've adjusted it to its full extension but there is still alot of slack. There is a bushing and adjuster assembly as shown in the Real OEM site and marked as for pre-6/86 bikes, presumably to retrofit the later cable, but it seems to be related to the bracket at the throttle bodies:

I wonder if someone's fitted a later set of throttlebodies? Most of them have an actuator (the bit the cable wraps round) that's 90 degrees (one quarter of a circle) but some have an actuator that's somewhere between 120 and 180 degrees. That one takes a cable with a longer inner.

Which makes me think: your throttlebodies may be K1100 ones. They have the bigger actuator and it's a cheap go-faster trick along with advancing the timing.

Picture please?

Dai wrote:I wonder if someone's fitted a later set of throttlebodies? Most of them have an actuator (the bit the cable wraps round) that's 90 degrees (one quarter of a circle) but some have an actuator that's somewhere between 120 and 180 degrees. That one takes a cable with a longer inner.

Which makes me think: your throttlebodies may be K1100 ones. They have the bigger actuator and it's a cheap go-faster trick along with advancing the timing.

Picture please?

I don't have any pics at the moment, but my problem is the opposite of what you describe. The replacement cable I bought has a longer free length than the original. I believe the actuator is a 90 degree unit. The bike mfr date is prior to the changeover for the cable,

By looking at RealOEM for a later model K100RS and comparing it to your 1985 model it shows that the only difference between the old and new throttles is the cable. 

In the parts drawing for the Bowden Cable the new cable requires parts 3,4,5, and 6 from the original pre 86 configuration.

So the question now is: Do you have the three parts that are at the lower end of the cable?  The bush, adjuster, and hex nut.

Point-Seven-five wrote:
So the question now is: Do you have the three parts that are at the lower end of the cable?  The bush, adjuster, and hex nut.

I do not. Either I will order them or fab something up. I do believe my replacement cable came with the handlebar-side adjuster (it was under the boot also supplied). IIRC then I might be able to modify that to fit the throttle-body side. Otherwise, I sketched up a part to be fabbed up out of either aluminum or delrin.

swampyankee wrote:

Point-Seven-five wrote:
So the question now is: Do you have the three parts that are at the lower end of the cable?  The bush, adjuster, and hex nut.

I do not.

I don't believe there ever was an adjuster at the throttle body end of the cable. Somebody here likely has an 'Brick in the '83 to '85 category so maybe that owner will let us know. If swampyankee looks closely at his updated cable at the point it enters below the front mast cylinder, he'll see those three parts under a rubber cover.  I think what might be needed here is a new cable holder at the throttle body end.

As I've stated, I DO have the adjuster under the boot at the bars. The question here is what parts are needed to fit the newer, longer cable since the 83 to 85 cable was superceded by the later, longer one. If i interpret the diagram at RealOEM that i attached to a previous post, it appears they are offering a different bracket, bushing and adjuster for the THROTTLE BODY end that will adapt the newer cable to an earlier bike. I will get a pic of the existing bracket this weekend.

swampyankee wrote:it appears they are offering a different bracket, bushing and adjuster for the THROTTLE BODY end that will adapt the newer cable to an earlier bike.

Appearances can be deceiving, especially when it comes to BMW's catchall diagrams. What they are likely showing is the group of parts needed when you replace an old cable that had an adjuster 1' from the top with an updated cable. If those parts all fit into the bracket, there would likely be a dashed line going through them from one to the other indicating connection, rather than a line beneath them indicating a group, mysteriously labeled 2 with no corresponding numbered line in the parts list. Interpreting it is all part of some Teutonic initiation rite, the outcome of which is never disclosed.

Anyway, like I said already, I doubt there was ever an adjuster down at the throttle bodies, but you might need a different bracket at the throttle body end and since there is only one offered now, that makes it easy.  Maybe somebody with an '83 to '85 will chime in and straighten out my thinking. Years of therapy haven't moved the needle much.

I have an eerie feeling this situation will be resolved with words like Oh, so that's how it goes together. 

Hi

The throttle cable with the adjuster a few inches from the handlebar was superseded by the current set up, which includes  bracket and other components for the throttle body end of the cable. Official BMW store will have the parts and they are not expensive. I have a 1984 K100 and I replaced the cable many years ago.
There is no adjuster, only a bracket. Parts diagram has all the relevant info. Good luck

Appearances can be deceiving, especially when it comes to BMW's catchall diagrams. What they are likely showing is the group of parts needed when you replace an old cable that had an adjuster 1' from the top with an updated cable. If those parts all fit into the bracket, there would likely be a dashed line going through them from one to the other indicating connection, rather than a line beneath them indicating a group, mysteriously labeled 2 with no corresponding numbered line in the parts list. Interpreting it is all part of some Teutonic initiation rite, the outcome of which is never disclosed.

Anyway, like I said already, I doubt there was ever an adjuster down at the throttle bodies, but you might need a different bracket at the throttle body end and since there is only one offered now, that makes it easy.  Maybe somebody with an '83 to '85 will chime in and straighten out my thinking. Years of therapy haven't moved the needle much.

I have an eerie feeling this situation will be resolved with words like Oh, so that's how it goes together. 

This makes sense. I'll get out there today and have a good look at the bracket in question, and see how it differs from the one pictured in the diagram. Essentially, there needs to be about 1" of extra space between cable end and quadrant to take up the extra cable free length.

Here's the cable stop bracket with mounting point in the background. I think I need to talk to the parts guy at Max and see what I need to install this cable. Just to show, here's a pic of the bracket alongside the control-end adjusters, the original and the one that came with the replacement cable. No difference in either. As-found, the original was at minimum extension. I adjusted them full out to compare lengths which are the same. 

So just to continue my attempts to start the bike, i bodged up an extension that tKes up the extra free play. I seem to have gotten it right for now since i have full motion of the throttle bodies.

Back to my regularly scheduled renovation, i installed new spark plugs and the bike fired up immediately after sitting for 3 weeks or so. It ran and revved great but it seems to be running rich. It stalled a couple times while i was trying to set the idle. The first time it wouldnt restart I pulled a plug and verified that I still have spark. The plug was pretty wet from trying to restart so I unplugged the fuel oump and it started. Plugged it back in and it ran good again but is blowing alot of black smoke when revved, which indicates a rich mixture.
Getting back to where I left off before the throttle cable debacle, I think I need to test resistance at the temp sender to both leads coming off as I understand one lead goes to the EFI controller.
Anything else I should look at to correct the rich running issue?

With the bike warm and idling press the green starter button. If the bike is lean the revs will rise, if  it's rich the revs will drop. A good mixture will result with the revs staying the same or a very slight increase.
Regards Martin.

MartinW wrote:With the bike warm and idling press the green starter button. If the bike is lean the revs will rise, if  it's rich the revs will drop. A good mixture will result with the revs staying the same or a very slight increase.
Regards Martin.

Interesting. I'll try that. though I expect the revs will drop due to rich mix.

Back at it today, I checked resistance at pin 10 which is the temp sensor. Cold it reads within spec. With fresh sparkplugs the bike starts right up and runs great. Initially it was pushing black smoke on revs which told me running rich. But I took it for a ride to the end of the street and it ran well. I shut it down and restarted several times and it ran well and revved pretty clean although it was idling up. While it was running at temp I tried hitting the starter button and it would stumble slightly so that would indicate a rich mix according to Martins post above.

In my frustration earlier I had "adjusted" the idle mixture screws trying to lean it out so I read up about it, and although I don't have carb stix yet, I set them all at about 1-1/2 turns out, which seems to be a universal starting point for everything idle mix related. No amount of adjustment seemed to make much difference - maybe the throttle bodies aren't closing completely. I shut it down to check oil and a few other things and when I tried restarting it wouldn't.  So I unplugged the fuel pump, got it running and quickly plugged it back in to keep it running. Since the oil smells of fuel I shut it down and while it was still warm (150f or so) I checked resistance at pin 10 again. According to spec it should be around 600 ohms. I couldn't get a good reading on it though - after initially reading in spec it kept going to 0.

So the mystery continues. Its kind of a catch 22 - I need to change out the fuelly oil before I run it any more, but until I resolve the richness issue I'll just be dumping more fuel into the crankcase trying to start it.
Would an out of adjustment TPS cause a rich start condition?

Check the vacuum line that runs from the #4 throttle body to the FPR for fuel leakage. A small hole in the FPR diaphragm can allow fuel to be drawn into #4 cylinder and fuel contamination of the oil. With enough fuel leaking into the cylinder this can cause a hydraulic lock and a destroyed engine.
Regards Martin

I've had that line off a few times and have seen no evidence of fuel leakage.
I'm tempted to just replace the temp sensor but that would be a parts-replacer approach to the problem as opposed to a more analytic approach.

You can try this:

http://dws.x10host.com/11tech/Rob.Lentini.Lean.Drop.MAF.pdf

So I just went ahead and ordered a new temp sensor, along with other maintenance-type items I needed. 

Question about the temp sensor - When I got the bike the wires to it were severed (P.O. said rodent damage but it was too clean a cut) and since they were same color   I reattached the wires randomly. I understand there are 2 thermistors in the sensor - one for the FI, one for the temp gage - but are they the same value? If I had the wires reversed could i be sending the wrong value to the FI?

No, the temp sensor wires go to Pin 10 of the L-Jetronic and Pin E of the white temp/fan relay in the relay box.. The temp gauge has a separate sensor in the bottom of the water pump.



Since the wire colors are the same they PROBABLY have the same resistance.

Easy to test. When you get the new one see if both pins have the same resistance between the each pin and threads at room temp. Then dip it in boiling water and check again to see if both pins have the same ohms.

I decided to pull the radiator, partly in preparation for replacing the temp sensor but also because the cooling fan isn't running. On the bench, the temp sensor reads relatively normal resistance at near freezing (no heat in the garage) on one contact. The other contact shows open circuit. Not sure which side goes to which but its knackered one way or the other.
I get no bueno from the cooling fan and upon closer inspection, the brush holders have melted at some point. Looks like I'll be replacing that while I'm in there.
While the tank is off I took a close look at the wiring and saw the rodent damage the P.O. told me about. Nothing chewed thru but some bare wires that i need to reinsulate.
And while I have the airbox out I extracted the Z hose. Definitely dry rotted, split and possibly incorrectly installed at some point
https://i.servimg.com/u/f32/20/47/74/09/20230210.jpg

That's a pretty common sight for the z-tube. You have two choices there:

1. by an OEM which will split again at some point
2. loop between the two spigots using a piece of silicon hose and a hose spring to hold it open.

I have it in mind to do (2) next time I need to replace one. Someone on here did just that a number of years ago, but as the pic. was part of another problem I have not been able to find it since.

As for the fan; again, pretty common damage. Don't bother trying to find another one. Most of us have done some variation of this:

https://www.k100-forum.com/t15052-spal-fan-installation

Great idea on the hose replacement. Too bad I already have one ordered.
But the Spal fan seems like a good solution to that problem. I just ordered it!
Between the Z hose and a new temp sensor, I have my fingers crossed it solves my running problem. After that it will be just a matter of synching and piecing the fairing back together in time for spring!