I have owned my 1985 K100RS for about 5 years now. Over the past 2 years, seems like it has had one thing after another wrong with it. It has 42,000 miles on it...was in pretty decent condition (at least it seemed to be) when I got it. It's gone from suffering random total system shut downs - which, after numerous helpful suggestions from y'all and researching other forum sites trying to solve the mystery, the problem was the ignition switch needed to be serviced/cleaned - to the most recent mystery problem: the bike now randomly stalls out. My bike mechanic friend ran some testing...he believes he found the problem in the Fuel Pump relay. So, to test it, he ran a hot wire  from the pos terminal of the battery to the left side of the Fuel Pump fuse slot. This seemed to be working okay for about a week, then the bike starting stalling again...even though the fuel pump was still running. AAARRRGH!!!

I really want to like this bike...it's a wonderful ride when it's working...but, I'm getting to the point that I am almost afraid of riding it...in the back of my mind, I'm starting to think "When will it stall next?", especially while I'm taking a curve/turn?

Does any one have any suggestions as to which of the more notorious switches, fuses, wiring connections, etc that I should be looking at?...not only just for the recent stalling issue, but also for potential future issues. 

Thanks in advance,

Rob

Others while chime in with more detailed and eloquent info im sure....but what your describing is to be expected on machines this old really (at least I reckon). As well as regular maintenance, theres the 1 in 30 year maintenance regime too. 

Set aside a day, get some cool beer, a chair with wheels on it, a shady clean spot, some tunes or podcasts, and proceed to methodically unplug each connector (one at a time) and thoroughly clean each one with deoxit. Each little contact must be cleaned. You will need to do this to the earth points under the tank too where the wires earth to the frame. You may even need some fine wet/dry paper etc to clean up some of the dirtier more corroded ones. 

there is a good write up on this procedure somewhere, use the search function, or maybe someone will post a link here.

Relays go bad, I had to replace a few. 

Also, recondition your starter motor. pull it out, pull it apart, clean it up and replace the replaceable thingys. (next on my to do list) as alot of the electrical circuit goes through the starter somehow or other and a failure here can cause all kinds of weird shit. 

Doing things like this will not only make your bike run better, but will help you understand its systems and logic and make you a better owner and maybe even a better rider. And its fun. And better understanding leads to better problem solving and pre-emptive repairs.

On top of floyd's suggestion, I would also do some hall sensor testing.  It doesn't sound like that's really the issue, but my old '85 would stall and cut out randomly and then one day just wouldn't start at all.  Replaced the hall sensor and was good to go.  You can find them used moderately cheap on eBay if you decide to do that.

There are ways to test the one you've got, but I'm not knowledgeable enough to recite them.  Maybe someone else will chime in.

G'day Rob , I agree with Rabid , early in the ownership of my KRS it was behaving like yours  , it turned out to be cracked wiring to the hall sensors at the front of the engine , definitely look there , 2 other things that stopped my bike in it's tracks were a loose ground connection to one of the coils ( dropped 2 cylinders ) this is not likely and a loose positive battery cable clamp , thermal expansion caused the clamp to loose connection when hot , rolling to the side of the road it would restart after cooling for 5-10 mins , silly fault but it happened ,

JR

A few simple checks, been there too.

1 If yours is the earlier fuel tank, the one bolted down under the front of the seat, you have a multipin connector into the front left of the tank for your fuel pump and level sensor. This can sort of become loose, if you open up the male pins a little with a precision screwdriver so that they make a tighter fit with the female socket under the tank. If this is loose you can get erratic disconnection and a stall due to lack of fuel. You can do this without removing the tank, you can pull the plug out at the front left and access it enough to open the pins. Later Ks have the plug at the rear on the right hand side.

2 The computer under the seat and under the headstock have multi pin connectors which can be an issue. Check that these are in good order, if there is a problem these can leave you with a disconnect. This can disrupt the signal from the Hall sensor. Even opening the connection and reconnecting can do this.

3 If its only happening when the engine is hot then a test is to heat the area around the Hall sensor with a hair dryer to heat it up. If the malfunction then happens on start up this may well be your problem.

4 Check on the cylinders it happens to by checking how hot the header pipes are. Don't get burnt though. If 1/4 as a pair or 2/3 as a pair go out then suspect a coil. Coils can fail when hot too, but if you find this swap the coils to be doubly sure. Also check the earths and connections at the coils.

The advice re the starter motor is excellent preventative maintenance. Its easy to do and also if you do ever get a breakdown you will find a starter motor is a very easy thing to replace or repair. They are extremely reliable but age is against them so this advice makes a lot of sense.

When I got my K last year I took it apart over a few days and did all these tasks, earths, connections, cleaned up pins etc and its really an essential thing to do. My RT is 84. I think they are remarkable for their age and extremely easy to work preventative maintenance on.

Two other points you'll want to look at/clean are the emergency/start button in the right hand grip and the contacts of the key switch, which both get dirty over the years. Use a plastic bag over it when you open them - little springs inside :-)

ReneZ wrote:Two other points you'll want to look at/clean are the emergency/start button in the right hand grip and the contacts of the key switch, which both get dirty over the years. Use a plastic bag over it when you open them - little springs inside :-)

Well spotted. There are posts on the kill switch doing nasty things. Also posts on loose bits or bad contacts in the ignition. That might show up on a steering position or riding over a bump.

Just looking through this and I would put my money on a hall sensor before anything else. It bears all the hall marks of what my K100 did when I first put it on the road.
There is a PDF about how to test them in the Downloads section, you will have to ask Bert AKA Crazy Frog for the password or possibly one of the Mods like Two Wheels Better. Once you get a pass word don't share or put up links to it just refer them as I have done here.

Looking back on the posts it seems the fuel pump is working fine.

The Hall sensor and the connections to the computers seem to be top of the list....try the hair dryer test, its called up in another thread, leave it on so that area of the Hall sensor gets warm as if the engine is warmed up. Then see if that reproduces the cut out.

Do you have one available to swap?

Or, when you're really tired of hunting down the gremlin at fault, sell it to a local. I'm sure someone will take it off your hands. In fact, I'm a local of sorts these days.

Seriously, it's likely a niggling little electrical fault or combination thereof, as the gents before me have suggested. Corrosion in the various connectors is the bane of early K bikes. But my money's on the hall sensor. They currently retail for $586 from US BMW dealers, part number
12 11 1 459 033, hall sensor with rotor in a kit, Vallantine's BMW Repair or KBikeparts (Duck) in Seattle might have a secondhand one, or I can get you a brand new unit for just under $400.

Is this the unit? I found it on ?Motorworks but they don't seem to list the item new.

Used - Ignition trigger unit | ELK59028 Fits K100, K100RS, K100RT, K100LT, K1, K100RS 16v, K1100RS, K1100LT
Larger Image	Mounted at front of motor under a T shaped cover. This unit works for all the 1000 and 1100cc four cylinder K series models. For the K75 version, please see [url=http://www.motorworks.co.uk/vlive/Shop/Parts.php?T=6&Q= ELK59049.] ELK59049. [/url] See [url=http://www.motorworks.co.uk/vlive/Shop/Parts.php?T=6&Q= ELA59028] ELA59028 [/url] for new option.	£48.00 No VAT payable Quantity 1234567891011121314151617181920 + Add to Wish List

Wow!!! Thank you all SO MUCH for your replies. You guys are awesome! I will definitely be looking at the Hall Sensor for starters...but, it also sounds like I will need to get busy on cleaning all of the wire connections...something, I'm sure, that has never been done in the bike's 29 years of life. I'll keep y'all posted.

please read up about "deoxit"  a known chemical cleaner of all electric connections with great results
there are hundreds of references in this forum about it

in the search bar "deoxit "

good luck

Rob, 

Firstly, no forum member has not been the title of your post. Relax and hang in there. The bike's old enuff to be from the Hoover administration. Wiring corrodes, rubber degrades. 

Note that in addition to cleaning contact points, DeoxIT is effective at cleaning wallets. For a fraction of the cost try a can of CRC 2-26 which is a fraction of the cost. It's found at Home Depot, f'rinstance. 


As far as diagnosing the Hall sensor...

Okay all...so, I went to Radio Shack and got a can of Deoxit and started a connecter cleaning session. When I pulled the gas tank off, the plastic multi pin connector (fuel pump / level sensor???) at the left side of the tank looked pretty worn (as can be seen in the picture). Could this perhaps be a contributor to my stalling issue?

In a word Yes. They are renoun for giving trouble as the age just like parents and kids.

Depending on what those two contacts closest to the camera do (power + and - ?), it looks like it was DEFINITELY loose and was wiggling around making a little spark with each new contact moment this burning the surrounding plastic.  The middle looks worse because it got it from both sides.  Just a hunch based on evidence.

It is most certainly contributing the issues you are experiencing. It may not be ONLY that, but you must certainly replace that plug.

There is an identical one in the relay box that you could pilfer if you wont be needing it (i think its for heated grips?)

Alternatively, it is a standard CB/ham radio female 4 pin connector, cheap and easy to come by and there are only 4 wires to solder and insulate - easy.

But seriously, replace it

The connector in the fuse box that's exactly the same is for an alarm system that 95% of k-bikes don't have.  Just be sure to cap off the ends of the wires when you clip it off.

Unfortunately, at least one of the wires (brown) is cracked about 3 inches below the connecter...and the other wires feel pretty brittle as well. Seems like I would need to replace the whole thing, wires and connecter. But, I can't seem to find what this connecter + wires is actually called so I can locate for purchase. I've typed in "fuel sensor", "fuel pump sensor", "fuel sending sensor"...but nothing has lead me to the correct item for purchase. Any ideas?

Mine just had the wires twisted together and taped!

I replaced both sides (plug and socket) with a generic auto parts 4 terminal connector. Soldered wires to plug and socket, not just crimped. Just make sure you match wires at plug and socket. 

Bill

My L T had the same problem with a previous owner. He got a new plug with wires on, cut off the old one and put a block connector on to connect the wires, taped the tank plug in place on the tank and located the connector in a very acceesible place.

My original post that was my no 1 risk item as I had the same on my RT but it wasn't burnt- spreading the pins a little cured it. Its been fine since. My money is on that being the cause of the problem.

I hope it sorts to so you can get out and about.

Short term cure is spread the pins a little with a precision screwdriver and see how it works for you. Also just check the female end in the bottom of the tank. This should stop the arcing that led to it being hot and also get you on the road.

indian036 wrote:Mine just had the wires twisted together and taped!

I replaced both sides (plug and socket) with a generic auto parts 4 terminal connector. Soldered wires to plug and socket, not just crimped. Just make sure you match wires at plug and socket. 

Bill

just be aware that any connector that is in a situation where vibration is an issue (almost all of a motor bike ) that soldering the connection causes issues ...in  that the solder (lead and tin based ) is particularly prone to cracking and eventual failure ...copper is far more malleable and will flex for far longer than lead or tin , keep in mind that the flux in the process of soldering wicks up the copper conductors ...and is a corrosive element ...causing failure also ..over time

almost all connections on vehicles are crimped for just this reason 

yes the soldering does work ...but for limited reliability over time ...unless you can isolate - support the joint in a non flex position
I must add that I have tested many soldered cables that appear to be conductive with the multimeter but fail to do their job ..usually because a crystalline connection has developed some where along the joint ..

just a heads up not a criticism

This is the early style fuel tank and connector.

You can not replace the male side as far as I know, as it is embedded in the tank. 

The corroded plug and brittle wires you wish to replace can not be bought from BMW as a spare part. you would need to buy the entire wiring loom as far as I know.

You can however go to Radioshack etc or ebay and buy a "4 pin female CB/Ham radio connector".

EBAY LINK


OR EVEN EASIER (As mentioned above several times...)

Take the tank off, delve into the relay box, locate the plug that looks identical to this one, but brand new....snip it off with plenty of wire, join it (solder or crimp) to where the old one was/is....roberts your mothers brother.

floyd wrote:
OR EVEN EASIER (As mentioned above several times...)

Take the tank off, delve into the relay box, locate the plug that looks identical to this one, but brand new....snip it off with plenty of wire, join it (solder or crimp) to where the old one was/is....roberts your mothers brother.

 Thanks again, guys.

Floyd, I did find that same unused/"brand new" connector in the relay box. My main concern is the length of wire needed to replace the old cracked, brittle stuff...I don't think there's enough on the connector in the relay box.  Looks like I may have to splice in some extra wire. I suppose I was just hoping that I could buy the whole kit and caboodle to make the clean swap.

Hey rob,

Websites like maxbmwmotorcycles.com sell electrical connectors.  I haven't checked the '85 k100 parts fiche, but they usually have a section in every bike's fiche for harness repair.  In that section, you can likely find a brand new replacement connector, probably with the right wires attached.  Hope this helps.

robdiaz44 wrote:... My main concern is the length of wire needed to replace the old cracked, brittle stuff...I don't think there's enough on the connector in the relay box.

Clip off the connector with as much wire as you feel safe to leave.  Insulate the severed wires in the relay box once you've clipped off the connector, using small pieces of heat shrink.  If you examine the metal sockets inside the connector housing with a magnifying glass, you'll see that they have a retainer in one of two forms.  Either it will be a single tab sticking out like the connector pins in this photo:


Or with wing tabs on the sides like in this drawing:


Use a very small flat-blade jeweler's screwdriver to get in-between the connector pin and housing, try an lever that tab inwards.  This will release the connector pin.  Do this for each of the four connector pins.  Now you have full access to solder on wires, the length of your choosing.  Fan the wires and then twist them together makes the surest mechanical connection with the least profile, like the diagram below:


Make sure to use a bit of heat shrink over the soldered joints.  Another way I splice in wires to existing connectors is to clamp the wire using the strain relief on the connector.  You'll notice, if you examine the connector, that there are a set of tabs that crimp over the wire and another set that lightly gip the insulation, forming a strain relief.  Use needle nose pliers to open the strain relief and expose the wire by removing the insulation (I normally clip off the existing wire to within 1/4" (5mm) of the connector.  I weave the new wire with the old and clamp the new wire using the strain relief.  This provides good mechanical security.  I finish off by soldering the wires together.

Use the jeweler's screwdriver to prise out the tabs so they can again do their job.  Insert the connector pin back into the housing.  It will seat with a click.

I do this all the time and it does not take a lot of effort or dexterity, just patience.

I know it's been way too long...busy schedule has kept me from working on the motorcycle. This afternoon, I finally dug back into the bike...focusing on swapping out the existing 4 pin connector (that connects to the bottom left side of the gas tank) with the unused one in the fuse/relay box. The wire colors on each of the connectors are completely different. I want to make sure I splice the correct wires together.

The old connector's wires are: green, brown, brown with white stripe, brown with black stripe

The one from the box under the fuel tank are: brown, brown with green stripe, blue with green stripe, red with yellow stripe.

Any help with the correct wire matchup would be much appreciated.

Don't worry about the colors of the wires on the ant-theft connector from the relay box. You've cut it off and those colours no longer figure into it, you'll just be using those wire tails to connect the tank wires. Just make sure the tank wires attach to the same position in the new connector as they did with the old connector using the indent in the side as a reference.

As mentioned previously, make sure you insulate the cut wires in the relay box with shrink or similar. Maybe put a tag on it for future reference so you or next owner know what those wires are for.

Depending on how close you cut the tails from the anti-theft connector, you can make your heatshrink long enough to cover the entire tail so that the 'wrong' colours don't show.

I want to thank all you guys again for your very helpful input and suggestions to get my ol' Brick back on the road. I replaced the fuel tank connector with the "spare" one in the relay box...started the bike up and did the hair dryer Hall Sensor test while it idled. It just kept purring along. Then, I took it out for about a 25 minute ride...varying from 25mph to 40mph street driving to opening it up with some quick acceleration on a highway, getting up to 60mph to 65mph. So far, it's running really nicely. Hopefully, the main issue was that faulty fuel tank connector.

Again...thank you so much everyone!