Hi, Im Nathan and I own a 1986 BMW K100- not sure which variant it is but it has given me 6 months of enjoyable trouble free motoring until today. I was wondering if I could get some help with it. Its my first big bike after passing my test and was just purchased as something to reliably and comfortably do a bit of distance on.



My real passion is for small 2 strokes so I also own this:


and this:

Welcome to the forum Nathan.  You seem to have done a good job nailing down the extremes of motorcycling -- very light to quite heavy.  Enjoys them all!  You suggest you need some help, but offer no specific problem with the bike.  In the event you merely need to be sure the maintenance is current on your newly acquired machine, there are plenty of resources here to help the new owner.  Look around. Ask questions.  We're a knowledgeable and patient lot!

The bike has been running great apart from a non functional speedo and fuel gauge but that hasnt really bothered me. The speed I can work out from the rpm and the fuel level from a glance inside the tank.

The fuel filler lock failed on me yesterday so I had to cut the pin on the flap with a small cutting disc on a dremel to get into the tank so it was subjected to a bit of vibration from the cutting and a few knocks with a small hammer in the lock assembly. I went out for a 50 mile ride afterwards and experienced no problems until today.



I went to start the bike today and it fired up with no problems to its usual tickover. About 20 seconds later while I was getting my gloves on the engine cut out without any warning. When pressing the starter button to fire it back up the fuel pump will still start as normal but the starter motor will not start to spin to turn the engine over. Tried a few times with no luck and left it for an hour, came back and it started up again, ran for ten seconds and then cut out again. Same deal again with the starter motor not doing anything. All other lights etc still work properly.

I tried a third time about half an hour later and it started again but this time only running for 1 second before cutting out.


I dont know much about these bikes but im assuming the ecu and other electrics are under the tank. How do I remove the tank and what is the problem most likely to be? A loose connection caused by yesterdays activity? Or an ecu problem that is unrelated. The bike has had a lot of electrical work done by the previous owners so a lot of connectors and earths have been replaced or modified.

Thanks

Dai and Comberjohn on the forum are not so far from you and have a wealth of knowledge about Ks. GMcQ is up that way too, Lisburn I think.

Incidentally there is an emergency fix for access to the fuel tank. a 3mm hold drilled 25mm back from the hinge, Sidecar Paul came up with it and it was tested recently. Drill that hole and plug it and you have an emergency release like the one in a cars auto transmission.

Tank on 86 has two lugs at the back of the tank with clips on them. Most people lose the clips. You have to disconnect the two fuel lines on the left side but be careful, the spigots on the tank can get broken off. The electrical connection to the fuel pump is on the right rear of the tank. The tank slides back and then lift off.

A word of caution, the fuel lines get hard with age and moving the tank around can cause them to crack so you should replace them as they are under pressure. BMW sell a length of fuel line, put the new ones a little longer and you can raise the rear of the tank to access the relay box without disconnecting the fuel lines, also you can slide it back to access radiator cap without disconnecting them too.

I had a similar issue as you with my LT. Cleaned all the earths, cleaned and checked all of the connections, cleaned starter motor, swapped load shed relay and starter relay. Last one I swapped was ECU at the headstock under the tank and it was cured after that.

well I returned to the bike this morning and it started up perfectly. It ran for 2 minutes on the stand and cut out again.Same symptoms as before.

Lifted the tank, the ECU units pins are in perfect condition as are the pins in the connector block that attaches to it. The 4pin tank connector is in good condition also.

My dad suggested that something inside the ECU could be breaking down in use and providing the situation that I have. Does this seem like a likely diagnosis? If it is I can order a replacement unit and hope for the best. Im willing to go that far but dont want to get into the trap of spending lots of time and money on the bike replacing components and sensors to see if I can find a culprit. I also dont want to disturb the wiring as it has been repaired in the past and everything is now quite brittle with age.


On another unrelated note under the tank I also found a few connectors with nothing plugged into them. Pictures are below. Could anyone please identify what they are for?

There are the two 2 pin connectors in the first picture and also a 3 pin connector held in place with the cable tie at the top left.






There is also this 4 pin connector towards the top of the second picture. Thanks again for your help people

fluffynat05 wrote: I also dont want to disturb the wiring as it has been repaired in the past and everything is now quite brittle with age.

Wiring repairs done by PO's isn't always that well done...........

fluffynat05 wrote:On another unrelated note under the tank I also found a few connectors with nothing plugged into them. Pictures are below. Could anyone please identify what they are for?

First pic: 3pin, hazard switch....spade connectors in T shape, heated grips....
the two connectors on top of the frame tube, no idea,,,former police?
whats the wiring colours?

Second pic: additional instruments.

On one of those the wires are brown and green/yellow
On the other the wires are brown and green/white


Ordered a replacement ecu from ebay and it should be here on thursday. Hopefully it will do the trick. I know the one that is in the bike at the moment was already replaced by the last owner as were the fuel injectors and some sensors.

Maybe these electrical parts are just getting to the age where failures are quite common, regardless of usage. On my old Hopnda NSR which was around the same age I went through 2 stators and 3 CDI's before getting components that worked properly

My guess is two unrelated problems that just want to plague you at the same time. The starter motor problem is most likely the starter motor relay. It won't be the starter switch because you've confirmed that the pump fires up. The other probability is a clogged-up fuel filter. If you don't know the provenance of the bike then changing the fuel filter should be high on your priority list anyway.

Someone else probably has additional ideas.

fluffynat05 wrote:On one of those the wires are brown and green/yellow
On the other the wires are brown and green/white

The two last connectors is for additional (head)lights.

I would agree with Dai about the fuel filter.
Should be changed as soon as possible. Mine blocked on me, complete engine fail while overtaking. Brown trouser moment.
It wouldn't restart until it was changed. Was blocked with particles from the fuel pump rubber damper that was breaking up.
Other thought that occurred to me. Have you tried seeing if it will run longer with the fuel cap open?
I remember that if the vent on the fuel cap on some bikes is clogged up, air can't enter the tank and a vacuum develops stopping the engine until it sits for a while.
Easy to check for.
I live in Clough near Newcastle if you need a hand with anything.
I've had three bricks and can bluff my way around them a bit.

There is loads of fuel flow from the tank when I pressed the starter button earlier with the fuel pipes disconnected. I will clean it out to be sure however.

The fuel cap is vented more than it would normally be anyway at the moment as I had to cut through the hinge to open it when the lock failed. Had a 50 mile ride like that with no problems.

to summarise:
1. hit starter button
2. bike fires up- runs perfectly
3. bike conks out a number of seconds later without warning
4. hit starter button again- fuel pump pumps, starter motor doesnt activate
5. leave bike for 30 mins
6. bike fires up again perfectly,starter working again, dies after a slightly shorter time period than before

7. leave bike for 18hours
8. Bike fires up and runs for a few minutes this time before cutting out
9. leave bike for 30 mins
10. bike runs for a second or two
11. the cycle repeats

after bike cuts out and starter motor doesnt work again it will not bump start either-suggesting that the whole injection system is offline too (unless these bikes cant be bumped)


why do all my bikes have to break at once? ARGHHHHHHHHHHHHH   lol
the moped is currently off the road so I can fit some bearings into its final drive unit- the shafts normally run in the casings with only a bit of oil as lubricant. fine for a standardish or lightly modified one, not so good for mine which regularly sees 15000rpm and has around 5 times the original power output. Also the lack of a stand, instrumentation and any lights whatsoever scupper any ideas of using it as a daily ride in the mean time.

The ape (thats the van) is also off the road till I can replace a suspoected broken ignition pickup or source coil and trundle down to the local MOT station at a not so steady 4-25mph and get another years ticket on it.

The backup backup scoot is currently in my bedroom and I dont want to have to disassemble the thing to get it downstairs just to rebuild it again for a few days use.

Likely a clogged fuel filter &/or errant sludge lurking in the tank itself. Classic symptoms you're describing. 
Allowing for time's inevitable toll I'd replace fuel lines, filter and give the tank an off-the-bike cleaning. Run Seafoam or such for a tank full or two afterwards. 

Signed, One Who's Been There...

fluffynat05 wrote:....

Lifted the tank, the ECU units pins are in perfect condition as are the pins in the connector block that attaches to it. The 4pin tank connector is in good condition also.

My dad suggested that something inside the ECU could be breaking down in use and providing the situation that I have. Does this seem like a likely diagnosis? If it is I can order a replacement unit and hope for the best. Im willing to go that far but dont want to get into the trap of spending lots of time and money on the bike replacing components and sensors to see if I can find a culprit. I also dont want to disturb the wiring as it has been repaired in the past and everything is now quite brittle with age.

....

The electronics come under suspicion quite a bit but are not often the cause of problems. FYI, there are 2 control units on the early Ks.
The Ignition Control Unit (ICU) is located under the tank just behind the headstock.
The Fuel Injection Control Unit (refered to as the ECU) is located under the seat accessible from behind the left side cover.
While the pins on both these may look ok it's a good idea to de-oxidised these and all other connectors and earth connections before doing any troubleshooting.
But I have to agree with suggestions above... sounds a bit like a fuel supply issue.

Questions:
1. When it dies, does it cough/splutter/hesitate first or does it just die like you turned the key off?
2. When its running for those few seconds, can you rev the engine smoothly above idle say around 2000 - 2500rpm

Cheers

I didnt realise there were two units. I ordered a replacement for the one behind the headstock.

1. when it dies its exactly the same way as if you turned the key off. NO coughing or spluttering or hesitation
2. when its running it revs and performs as smoothly as it always did. When I tested it earlier and it ran for 2-3 minutes the engine responded correctly and was still happy past 5k rpm.

Its worth noting that with with a 30min rest it ran only for a second or two, with an hours rest it ran for 10-20 seconds,  and with an 18 hour rest it ran for 2-3 mins.

trying to start it within 30 minutes and no luck-no starter motor action but a yes to the fuel pump working. I removed the tank immediatly after one of the times it cut out and the lines underneath were still full of fuel.

It doesn't sound like its getting starved of fuel but that doesn't mean its not. Its puzzling???

I'm off on a different tack here... Try checking the battery. How's the electrolyte levels? Take a voltage reading with a multimeter set to DCv around 20v range with ignition key off then a reading under load... turn on anything that uses power like lights. Alternatively take the battery out and get it to a Battery shop and get them to test it.

Could be you're losing power to the ignition system somehow. Someone else might like to chime in at this point???

EDIT: Dai suggested the starter relay above. Would be worth taking a look at that. Its easy to open up. Its in the R/H rear corner of the elec box under the tank.

When we had the problem with the K75 the guy thought it was a fuel supply issue too [which in a sense it was as it was an electrical connection]. But when I wriggled the unit under the seat the problem solved itself. I am not sure what was what but it was a bad connection from the multipin connector, it seemed to interrupt the fuel supply. The engine would stay running if we kept the starter button pressed which had told us we had a good fuel supply from the filter/fuel pump. It would also rev freely without spluttering. We cleaned up all the pins on the ECU under the seat and very slightly adjusted those we could not see a tell tale shiny line indicating a good electrical connection.

On the other hand when I had a problem on the LT there was no response when pressing the starter button and after changing relays and cleaning earths, connections etc it took a swap of the unit under the headstock to cure it. Oh, the fuel pump did work when this happened.

Welcome from sweltering Johannesburg

Hi Olaf

Easily explained. Pin 8 on the ICU connects to pin 1 on the FICU; also pin 7 on the ICU connects to pin 85 on the Fuel Injection relay. Corrosion or a poor connection on either link will kill the system.

A clean shut down indicates an electrical issue.  The fact that the longer the engine sits the longer it runs on the next start indicates it is probably temperature related.  Hall effect sensor?

Just my $.02.

Maybe I've missed it in the thread but have you checked if there is a spark after it cuts out? Pull a plug cap off and hold a plug against the head and see if it sparks when cranked over.
Should rule out 50% of the potential problems.

Just to throw another possibility into the ring......

I've recently had a few starter button issues. I've got to recognize it immediately now, but at first I was sure it was electrical. I have on a couple of occasions had the bike sit in a heavy down our, my rubber seal has long gone on the button. water and or road grime has got down into it and occasionally the starter button stays on (or worse comes on). It doesn't run the starter motor but suddenly enriches the fuel mix so it dies. if it happens under acceleration it can get quiet exciting and embarrassing.

When it first happened, I was sure it was either electrical interruption, or fuel starvation.

Just worth a look. 

Jez.

Also, if you haven't looked at it. there are some great links in the portal.

So you bought a K bike, and the wiring diagrams.

It can only enrich the mixture if the neutral light is on or the clutch lever is pulled in.

Thanks Rick,

That'll explain why it gets me at the traffic lights. I imagine then also that an intermittently nutso gear position switch would only compound the issue?

jez

Comberjohn wrote:Maybe I've missed it in the thread but have you checked if there is a spark after it cuts out? Pull a plug cap off and hold a plug against the head and see if it sparks when cranked over.
Should rule out 50% of the potential problems.

I was thinking that also but ruled it out because the starter won't turn over till its good and ready. Then it starts and runs for a short time. Sounding more like the starter relay to me.

Jez wrote:Just to throw another possibility into the ring......

I've recently had a few starter button issues. I've got to recognize it immediately now, but at first I was sure it was electrical. I have on a couple of occasions had the bike sit in a heavy down our, my rubber seal has long gone on the button. water and or road grime has got down into it and occasionally the starter button stays on (or worse comes on). It doesn't run the starter motor but suddenly enriches the fuel mix so it dies. if it happens under acceleration it can get quiet exciting and embarrassing.

When it first happened, I was sure it was either electrical interruption, or fuel starvation.

Just worth a look. 

Jez.

Also, if you haven't looked at it. there are some great links in the portal.

So you bought a K bike, and the wiring diagrams.

Jez. I had the same problem. Worth fixing that to avoid any problems on-the-road. Here's how I rigged a new cover button.
https://www.k100-forum.com/t8541-replacement-starter-button

Did it Kaptain,

I think it got  down the back of the switch (crack in the housing at the top) have now lost my plunger and got silicone down the shaft of the switch. Nothing is very pretty there at the moment.

Jez wrote:Thanks Rick,

That'll explain why it gets me at the traffic lights. I imagine then also that an intermittently nutso gear position switch would only compound the issue?

jez

Hi Jez, here's another SCP clever idea (bodge?) that may help with your gear indicator.

https://www.k100-forum.com/t6936-gear-position-switch

Paul

That's fantastic,

Thanks again Paul.

Jez.

Hijackers!  

Anyway, back to the business in hand.....Welcome to the Forum Fluffy. That's a nice clean K bike. Hope we'll see you out'n'about on it on one of our runs.

Duly admonished 88!  

So,   to the World's best forum Fluffy, enjoy your time here.

Paul.

Indeed.

Welcome aboard the K Bike express Fluffy, there's nothing about your bike you won't find here.

Jez.

Just a quick update. Fitted a replacement ecu today and fired the bike up and it ran great. I got my hopes up and left it running, unfortunately 10mins later it cut out again.

This time the starter worked immediatly afterwards however unlike the last time. I tried a few times with the starter and it coughed a bit. Gave it a rest for 30 mins and went back to it. It cranked over but showed no signs of life. I unplugged one of the ht leads and stuck a known good spark plug in it from another bike and rested it on the cylinder head- cranked it a few times and no spark.

So the ecu replacement sorted whatever was originally wrong and now something else has gone wrong. I dont have the time to diagnose further issues or replace any more bits as all money is tied up in the scoot and the van. I think im just going to sell it,save the money up for a bit and pick up something else that will do as a runaround. Not too bothered about engine size so long as its greater than 125cc and can ferry me and a passenger all round the country this summer.

Its a real pity but I did get an enjoyable 6months out of a nice to ride bike with no hassle which was good. If anyone on here is interested in it let me know. There is 6 months MOT remaining on it.

Thanks again for all your help so far.

Nathan

Nathan,

That's a real shame. They are great bikes and when things go wrong they usually can be fixed relatively inexpensively. 
There's a huge wealth of experience both here on the forum and very close to you in Northern (and Southern) Ireland and with a little time and patience, I'm sure you'd find the fault affecting your running and get her going once again.

However, totally understand conflicting priorities and limited funds - space can be an issue too. It's always a hard decision.

Best of luck with selling on. Hope she goes to a good home.

You'll not find a more enjoyable motorcycle to "ferry a passenger around the country this summer" and you know it! And you'll lose money on it by selling it not running. Worth sticking at it imo.

Definitely electrical but I think buying another ICU was premature (don't thro the old one away just yet). The K-beast electrics are a little quirky so I don't think "something else has gone wrong". Likely there's a couple of issues in the mix.

• Contacts on the ICU and ECU. You've not said if you had cleaned these. They BOTH really need deoxidising. You should be able to buy something like Deoxit locally.
  
• If there is no spark and it won't even try to start without even a cough then it's not likely to be the coils. Both coils going at once is unlikely. The coils rely on a good earth so well worth taking the earth connections apart, cleaning well and deoxidising also. The main one is under the tank on the left of the main spar and another on the GB just above the left foot peg
  

Failing that, I would be testing coils and HT leads. There's a good thread here to walk you thru that.

These things together would take less than an hour and the cost of some electrical cleaner.

Hang in there fluffy :albino:

The bike went away today, buyer is going to spend some time doing it up.
Quite handy really as yesterday my angle grinder exploded,and the inner tubes on the van disintegrated and rims were rotten from the inside when I went to change the back tyres. The money will be handy for sorting that out and saving up for a replacement bike.....or some more go faster parts for the scooter

Well, I hear that she has gone to a good home...ride safe and hope to see you back on here when you've had enough scooting about and fancy a bigger bike again.

Yeah - it's crash-landed about four hundred yards from me!!

spotted a little honda vt500 today, it looks promising. Never had a v before so would quite like to try one and see what they are like

Hope it works out well for you Nathan but any older bike is going to have issues and from experience you would find getting parts for an older Honda far harder.

fluffynat05 wrote:spotted a little honda vt500 today, it looks promising. Never had a v before so would quite like to try one and see what they are like

My first bike after passing my test was a Honda VT500. Nice enough bike to ride and considerably lighter than the K's (but what would you expect - it's half the size).

The V twin arrangement works well, I don't recall any vibration problems but is a right PITA to change the spark plugs etc because of the orientation. 

Sadly mine started burning more oil than fuel (only did about 20 miles/day on it) and in my enthusiastic ignorance, I decided to strip her down and fix her. Long story short, the price of the bits exceeded the value of the bike and while saving up for these bits, I had a work bench malfunction that resulted in all my carefully arranged (but not bagged and tagged) components and engine crashing to the garage floor and getting thoroughly mixed up and confused. A few months later, I had to move house for work and I knew that the box of assorted VT500 pieces was never realistically going to ever become a bike again. A local bike breaker rudely offered me a few pence for the bits, so I took the whole lot to the council tip and chucked it in the metal recycling bin!!

Think that might have been the ultimate fate of this particular brick.
Gave it a quick wash this morning. What a difference!
Far from mint, but I can see a bike there now.
If you're still dipping into this thread, Nathan, you may have regrets about selling it. Too late!
Jap bikes are generally so unsatisfying.
They used to call British built cars from the 50's and 60's 'gray poridge' because they were so dull. You could call a lot of the Jap stuff from the last 30 years the same.

When I was writing for most of the (UK) monthly bike mags back in the Nineties we referred to any bike built in the 50s and 60s and under 500cc as 'grey porridge'. I wonder who originated the term?

Dai wrote:When I was writing for most of the (UK) monthly bike mags back in the Nineties we referred to any bike built in the 50s and 60s and under 500cc as 'grey porridge'. I wonder who originated the term?

Dai, I think it was 'One Track' who used to write for Motorcycle Sport (and MPH, the Vincent OC magazine).

Paul.

A number of years back a new magazine came out, called Mercedes Enthusiast. I took to it and was mighty impressed to be taken back to the great road tests of the early seventies when I opened it to read some very well written road tests by none other than LJK Setright. Unfortunately some years later he passed away.

Now I wonder would Dai and more of us remember his rides on Honda fours, Suzuki Kettles etc etc.....

SC: I thought it might have been Radco, but on reflection he was too much of a gentleman to turn a phrase like that.

Olaf: I never met LJK because I was a freelancer rather than an employee, so we (effectively) moved in different circles.

Just a quick update on the fate of Nathan's K100.
Also, I know he has been dipping into the forum now and again. 
There's no known cure Y'know.
Haven't done much to it but it is now a reliable runner in the true spirit of a K100. Starts first time, every time.
The problem?
It had a home made immobilizer consisting of a key switch in the tail unit and a series of wires to a rather damp, metal clad relay.
Cut it all away and no more running problems.
Seeing as it still has an MOT, I'm thinking of giving it a service and a tart up and maybe putting it on the road now and again this year.
There's always next winter for a rebuild. 

Good to hear it's been saved John.

excellent, good to hear its working again and will get a bit of use. Dont think I would have been able to diagnose that immobiliser issue myself.

Hi Nathan. Knew you couldn't stay away!
Decided to go ahead with the rebuild anyway.
It's a bit lighter than it was this morning.

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