I realize that this forum is dedicated to the trusty K100 and I have a 1984 one of those also. The problem I am having however is with my 1993 K1100LT. I took a leisurely early evening ride out to a local beauty spot two nights back and on my way home I hopped onto a dual carriageway road in order to get home for an appointment. Bike was running flawlessly at this point. I was getting harassed by an Audi driver so I decided to leave him well behind and hit the gas quite hard. All of a sudden I was missing a cylinder and running on only 3 - I managed to limp the bike home and park up for the evening. My first thought was that it was a failed spark plug, as I have not changed the plugs in nearly two years and I ordered some replacements from Motorworks. Today I got around to fitting the new plugs (the old ones were in a terrible state with hardly any central electrodes left at all and one at least seeming to have a light grey deposit almost crossing the plug gap, however they all showed signs of a good mixture and clean burn etc.) I did notice that upon tapping the spark plug caps that there was an awful lot of whiteish dust/powder that came out of them! When I had gapped the new plugs - NGK DCPR7E - and came to fit them, it did seem to me that, although the rubber boots seemed a good snug fit, the inner connection was not all that good at all. I wondered if all the dust that I had knocked out had perhaps been oxidised aluminium etc. and that the plug caps were not so good. Anyway, with all 4 new plugs in place and all HT leads reconnected correctly I hit the starter button. Damnation !! The bike is still only running on 3 of its' four cylinders ! Any suggestions as to the possible cause of my continuing problem would be warmly welcomed from the knowledgeable members here

A troubled injector?

Maybe put some techron/injector cleaner in the tank.
Run it for a bit...and then put some more in there. ?
...and put some more in there.

Did that for mine in the last year....x4

Was giving 38 mpg and now is at 43.


Also might want to check that the little rubber caps on the fuel rail are all there.

Found that one was missing, up front, that couldn't see previously because of the fairing.

When bike was idling, stuck finger on the same, felt suction...and said, "This isn't right"...

Capped it off and the bike immediately started idling better....

Dunno if any of this might apply...
Wish you the best though.

FWIW.

Have a good look inside the plug cap and if it is to the point of failure then it should be obvious.
Try swaping plug leads so that you are using a different lead for the cyl that is missing plug lead 1&2 can be used for either of those plugsand so can 3&4 but of course you need to swap at the coil as well then if the miss moves to the other cylinder there is the problem. As for the white powder well thats what you get if the cap is arcing.
Did the plugs that came out have the bobbins on the top and have the new ones got them on.

RicK G wrote:Have a good look inside the plug cap and if it is to the point of failure then it should be obvious.
Try swapping plug leads so that you are using a different lead for the cyl that is missing plug lead 1&2 can be used for either of those plugs and so can 3&4 but of course you need to swap at the coil as well then if the miss moves to the other cylinder there is the problem.  As for the white powder well that's what you get if the cap is arcing.
Did the plugs that came out have the bobbins on the top and have the new ones got them on.

The old plugs did not have the bobbins and so I assumed that was the way the new plugs should be also and removed the screw on bobbins from the new plugs prior to fitting.

Thanks for your input re. swapping the coil leads etc. but at the moment I am unsure which cylinder is not firing correctly - until I work that out I cannot try that method.

JimK wrote:A troubled injector?

Maybe put some techron/injector cleaner in the tank.
Run it for a bit...and then put some more in there. ?
...and put some more in there.

Did that for mine in the last year....x4

Was giving 38 mpg and now is at 43.


Also might want to check that the little rubber caps on the fuel rail are all there.

Found that one was missing, up front, that couldn't see previously because of the fairing.

When bike was idling, stuck finger on the same, felt suction...and said, "This isn't right"...

Capped it off and the bike immediately started idling better....

Dunno if any of this might apply...
Wish you the best though.

FWIW.

The injectors are on my list of things to check - thank you for your input JimK

I didn't get time today to investigate my issues further but I need to isolate which 3 cylinders are working correctly and which one is not. I figured that as she will start and run on 3 cylinders ok that I would then pull the plug leads one by one and see which one made no difference to the running. At least that way I can narrow down which area to look in. Is this a good plan to narrow down the faulty cylinder/lead/HT cap etc ?

Not a good idea to pull a plug lead while running, not only are you more likely to cop a 80000 volt zap but you may fry the ignition due to high voltage spikes feeding back through the primary windings of the coils.

If it is only running on 3 cyl then it is highly unlikely to be the ignition at fault because of the wasted spark system when #2 & #3 fire together at the top of each stroke as do #1 & #4. If you did pull a plug lead you would get a bad indication weather it was the bad cylinder or not.

I would be looking at plugs still conducting but not arcing and air leaks below the butterflys mainly the O ring under the manifold stub and around the injector. Air leaks futher back don't cause rough running problems in a motronic system.

Perhaps you can get a neon spark tester like this:

http://www.thetoolwarehouse.net/p-15941-lisle-19380.aspx

That will indicate if the plug is firing, but would not indicate if the cylinder were missing because of a lean condition.

You could get an infra red remote thermometer like this

http://www.harborfreight.com/non-contact-infrared-thermometer-with-laser-targeting-60725.html

point it at the individual exhaust pipes.......should find the cool one immediately.

If you want to find which pipes are hot just very quickly flick your finger across them fast and the slippery ones are hot and by fast I mean fast. I have been doing it that way all my life and have never has even the slightest burn.

If you are running on three cylinders instead of 4 you have good coils [assuming the connections to the plug leads are good...] and you should look to the cylinder specifics: plug, plug lead, injector in that order. Before even going near injectors you have to make sure all the wiring is good as in connections. If its running on 3 you have fuel in the rail so no looking at the fuel circuits.

I got back to this problem briefly this afternoon and tried my original suggested diagnostic technique.  Started the bike up with a little persuasion and still apparently only running on 3 cylinders etc. Grabbed a pair of insulated pliers and removed each plug cap in turn - going from the front of the bike/engine removing plug cap 1 resulted in even worse running condition but I could clearly hear good strong spark from cap to plug, same with plug cap 2, however when I reached plug cap 3 and applied the same method there was no change in running condition - however there was a good spark at the plug when i tried the same test whilst earthing the plug (connected to its plug cap) to the head ! Removing plug cap 4 produced worse running condition once again.  To me this suggests that the problem lies somewhere in cylinder 3 without doubt.  I am unsure what the problem could be and how to move on from this.  Could it be a stuck valve/bent valve stem, holed piston or a witches curse !  I look forwards to any further input from our mechanically/electrically gifted membership

RicK G wrote:If you want to find which pipes are hot just very quickly flick your finger across them fast and the slippery ones are hot and by fast I mean fast.  I have been doing it that way all my life and have never has even the slightest burn.

Great way to get rid of your fingerprints and end up with smooth fingers should you ever embark on a life of crime!

lol
yes that does work

I regularly have to enter work place premises with finger scan technology ...but my mechanical skills leave my hands in a poor state of repair for the scan
often rejected
bummer !

Take a look up the spark plug caps to see if the bit that grips the lug is 2mm in diameter or so or about 4 or 5 if 4 or 5 you need the bobbins on the top of the plugs. Then do a compression test to check all the cylinders have good compression, when you take the plug out can you smell unburnt fuel in the cylinder? Try swapping a lead from a good cylinder to the bad cylinder is it then running on that one?
Regards,
K-BIKE

Give it a compression test and if that is OK then it is fuel.

Compression test is next on the list - front brake master cylinder has just failed on my K100RT today too - it never rains........ So I now have 3 motorcycles and cannot ride any of them - grrrrrrrrrrrr !

might be one dodgy fuel injector....possibly one of the easiest fixes too....hope it all goes well ..

Sadly only one of my bikes is fully functional now - I managed to source a new front brake master cylinder assembly locally for the BMW K100RT and have successfully fitted the above, bled the brakes and all is now functioning as BMW intended back in 1984 when the machine left Bavaria.  I got around to running a compression test on the BMW K1100LT today and cylinder number 3 has zero compression !  This means that major/expensive work will be required to ever get her running again.  The Kawasaki KZ1100, whilst fully functional, has been on SORN (declared off the road) for the last 18 months and needs some work to make her road ready again.  It seems ironic that the highest mileage bike (BMW K100RT @ 108,000 miles) is still proving to be the most reliable of the collection - it never rains but it pours

Sad news, major work ahead.
All this because of that dude in the Audi.
At least the old RT is there.
You'll fix the LT, plenty of good advices here for that job.

There's a slim chance that one of the exhaust valves on the dead cylinder has receded & become so tight in clearance that it won't seal. I would advise checking the valve clearances on that cyl at least and see if any one has no clearance. If so. you might be able to re-shim it and get some more service out of the engine.
Another possibility could be a broken or collapsed valve spring though I personally have never seen that.

More likely>>>>
One member here recently had a broken exhaust valve where half the head fractured off on a 16V model & I recently took a cyl head off that had a single (8V) exhaust valve about 50% burned away at 235,000 miles.
It could be worth some inspection anyway before going through the time & expense to remove the cyl. head.
Regards, Ibj...

Thanks for your input ibjman. It would be nice to think that a relatively simple (cheap) solution could be found. Sadly I do not have the facilities to much more than basic diagnostics. Could what you have suggested be checked without removal of the engine ? I am happy enough to strip all the fairings/plastics off her if I can attempt further diagnostics/repairs without engine removal

Check the valve clearances and if they are ok then you virtually have no choice but remove the cylinder head to find and repair the problem. You shouldn't need to remove the engine as I will say the most likely explanation is a bent valve in which case the clearance will have opened up a lot. Mine broke a piece from the valve but that is a highly unusual occurance.
Before you do remove the head squirt a heap of oil down the bad cylinder to see if you get any compression which I will say is unlikely. If there was some compression that would mean a ring or piston problem which still means head removal.
If you have a bent or busted valve I will send one of my valves from the old head with no guarantee but as against 88 quid for a new one?

JimK wrote:Maybe put some techron/injector cleaner in the tank. FWIW.

I use injector cleaner faithfully with every oil change.

More to the point, just bought the bike last year, and when I replaced the spark plugs this winter noticed the same grey dust coming out of cylinder #4 plug boot. It seems the little spindles were missing (NGK plugs), normally one has to transfer them over from a set of Bosch's, and the dust was building-up under the boot, I believe, from a faulty connection.

so I decided to leave him well behind and hit the gas quite hard.

Without that comment I would be looking at anything to do with spark to no 4 cylinder. I am presuming the K100 also uses the wasted spark.....The plug lead should be interchanged with one of the others, possibly swap 1 and 4 on the coil if that is possible [that works on K100].

The gray being there for some time points to some long term electrical problem.

The plugs do seem to fail quite a bit, cheap but it happens so never assume a new one is 100%.

Injector problem is only an issue if the plug lead swap does not work unless the problem has occurred up in the ECU controlling the injector.

The only time I ever had top end trouble was a car towing a boat and trying to keep up with some more high powered motors. Burnt a valve. If your fuel mix was off that is a possibility as is being pointed out. Not a bad job to sort.

You can get a camera to go in the plug hole too, if you know any friendly engineers.........worth a look.

92KK

RicK G wrote:Check the valve clearances and if they are ok then you virtually have no choice but remove the cylinder head to find and repair the problem. You shouldn't need to remove the engine as I will say the most likely explanation is a bent valve in which case the clearance will have opened up a lot. Mine broke a piece from the valve but that is a highly unusual occurance.
Before you do remove the head squirt a heap of oil down the bad cylinder to see if you get any compression which I will say is unlikely. If there was some compression that would mean a ring or piston problem which still means head removal.
If you have a bent or busted valve I will send one of my valves from the old head with no guarantee but as against 88 quid for a new one?

Thank you for your advice and offer etc Rick G - when time permits I might try to carry out the works you have suggested

I hope you don't mine me resurrecting an old thread, but I found this while searching for enlightenment on a problem I had.
What happened to the OP, is a carbon copy of what happened to me a couple of months ago.
So much so it's quite creepy.

I too was out on a stretch of dual carriageway on my recently acquired K1100RS, and like the OP, got into one of those stupid pi**ing contests with a car, which in this case was a Mercedes.
I was really hammering the poor old girl, when suddenly, I lost power.
Long story short.
I limped home on three cylinders, and quickly determined complete loss of compression on number two.
The plug from that cylinder was a molten mess.
There was also coolant splatter over the little heat shield that sits under the left foot, which also ran up the length of the silencer.
Off it went to the mechanic I use for head off inspection, which revealed both exhaust valves completely buggered,
They looked like someone had taken a chisel to the edges of them.
The other cylinders were all fine,
The bore was also scratched in number two, so that was that.
I had to do a lot of soul searching, and in the end decided the bike was way too good to scrap, so I sourced another engine, (James Sherlock) and got my mechanic to fit it, and now it's running lovely again.
The problem I have is that it could not be determined what the cause of the catastrophe was.
My wrench went through everything with a fine tooth comb, and the only thing he found which could have been a contributory factor was the fuel rail, which was badly corroded internally.
So much so that he flatly refused to re fit it, so I got a new one from BMW which came out to quite a reasonable (for BMW) £55.
He did a test on the injectors which came out good, fitted a new fuel filter, checked the valve clearances on the replacement engine, and fitted a new air filter,
Luckily I got the bike cheap, but even so, with the replacement engine and related labour and parts costs, she now owes me well over 2 grand,

For me though, this was a price worth paying, and it's running brilliantly.
I've done 400 miles or so since the re fit, and have looked at the plugs which are all consistently good and the same colour.
So my confidence has taken a battering,
I was planning a trip to Italy on her in September and I hope it's come back before then.
I love this bike, which I have clearly illustrated here, and maybe I just have to accept that the likely cause of my troubles was simple over revving.
As you can see, this is more or less exactly what happened to the OP of this thread, and assuming he is still here, I would love to know if he got to the bottom of what caused his problems,

Only one thing - Rick mentioned it but didn't elaborate - check the inside of the HT caps to make sure that they're intact and not a mass of corrosion. All four of mine were completely buggered but I only found the problem when I got fed up with an intermittant misfire! If you find that you need new leads, forget BMW. Go to realmengineering.com - less than half the price and far better quality than OEM.

I broke a piece of an exhaust valve, a half moon shape but fortune smiled and apparently the bit went out red hot and did no damage.
I was doing 245kph according to the GPS when it happened and I would say it was when I shut it down for a rapidly approaching corner as I stopped just after the corner and when I restarted after the slow ones caught up it ran on 3 cylinders.
That makes 3 in very similar circumstances now so I think sticking to only 150% of the speed limits will save this engine from a similar fate.

I am wondering if it was just a simple case of over revving.
Do our old K bikes have a rev limiter ?
If not, then that could have been it because when the red mist descended I wasn't paying any attention to the rpm

Rick - if that's three gone the same way for the same reason then I'd say what is being described is 'shock cooling', except that it's not supposed to affect liquid-cooled engines as much as air-cooled ones. It's a big problem with air-cooled Lycomings; suddenly pulling the throttle just before or during a descent is almost guaranteed to wreck one or more cylinders.

bikesnbones wrote:I am wondering if it was just a simple case of over revving.
Do our old K bikes have a rev limiter ?
If not, then that could have been it because when the red mist descended I wasn't paying any attention to the rpm

They are rev limited to 8700rpm and will retard the ignition timing about 200rpm before they cut the injectors.