Slightly less power as in "leaner", or reduced IGN timing?

Possible. My point was.....it may have achieved those goal by changing the factory fuel mapping.

If so, The adjustments to the CO and TPS may need to be outside the normal spec to compensate.
All Hypothetical.
As we go I'll learn more about going back to a point in time when this first began.

Yes, as in leaner. The description of it says it increases fuel economy by around 3-4 mpg and is a simply plug-n-play install, no tuning or adjusting necessary. Nothing would have to be adjusted outside normal spec. Still a possibility though. Although, my mileage is usually around 31-35 mpg around town, which is pretty bad. I told this to a BMW mechanic, and he placed the blame on California's awful quality of gasoline.

I don't really remember when it first started, it was likely gradual until it got worse to where it is now.

Came home and turned the CO pot about 4-5 turns counter-clockwise from where it was when I had bad injectors. It helped quite a bit, so here is an update video for comparison with the last video I took of it:

NEWEST VIDEO:
https://youtu.be/pC4phjxKFec

older video:
https://www.youtube.com/watch?v=BfVbiyWS5Tg

So any news?
I just got me a 94 K100RS 2 weeks ago. (56k miles) and having VERY similar issues.

Cold start fine.
Ran 1.1/2 hrs at 60- much higher up motorway  no problems
stopped for petrol and stuttered out of the service area. seemd to be going on 2 maybe 3 cylinders and then cleared itself.
Makes riding bends/roundabouts (I appreciate not a big issue in USA) difficult. as you tramp in aat a good speed, rrake, blip and down change and then it bogs down as you try to drive out.
when its 'bad' its got a lumpy tickover at around 700rpm. cold its a nice smooth 1k and reacts nicely to the throttle.

I'll try the obvious issues  but I'm keen to see what the solution is here!!

Hey welsh,

I wasn't aware they made the k100 past 1992.  Sounds exactly like my issue though.  I've gotten it to a manageable point where it actually runs pretty good.  Here is a list of everything I did:





Description of issue:
----Engine misfires from 1k to 3k RPM.  Misfire does not occur when engine is cold.  There is a hesitation in power around 3k RPM.  Misfire is most apparent when engine is held at 2k RPM, and sometimes (infrequently) a somewhat loud "click" sound occurs followed by a temporary drop in RPM (without moving the throttle).  The misfiring seems to stop after the power hesitation and the engine runs well and smoothly above 3k - 3.2k rpm.  The misfire occurs under power (in gear / moving) as well, with somewhat noticeable drops in power.
----Maybe once a week or less, the engine will give a loud backfire out the tailpipe.
----There was a time when the bike ran correctly, with little to no misfiring.

Things that have I've checked / replaced:
-New FPR installed
-New spark plug wires (NGK, non-metal caps)
-New / correct spark plugs installed (Bosch XR5DC)
-New fuel filter and in-tank hoses
-New Injectors (Bosch Type II) - helped a lot (I believe bad / very dirty injectors were the main problem)
-New air-related rubber parts all around

-Cleaned fuel pump pre-filter and sucked out some dirt from gas tank via a syringe
-The chip in the Motronic computer is stock BMW, not aftermarket.
-TPS adjustment (setting to 0.5v helped issue, currently set correctly at ~0.375v)
-CO potentiometer adjusted to max idle then back a turn

-checked coils for jumping sparks (none, even when doused with water while idling)
-synced all TB air bypass screws (helped. used one vacuum gauge, so not precisely)
-bit of oil consumption, probably not cause of misfire (maybe a quart per 1300-1500 mi.)
-no noise associated with misfire aside from the infrequent 'click' sound at ~2k rpm
-re-applied heatsink paste (liberally) to the ignition amplifier
-air filter is new (about 1.5k miles)
-no air leaks apparent.  replaced ALL rubber intake system parts (except the hose on the back of the TBs)
---also replaced plastic intake boots and O-rings (cleaned engine surface beneath boots prior to installation)

-measured resistances / voltage of components at Motronic connection pins (all normal)
---one of the resistances from the CO pot was different from the other, but I think that is due to the tachometer being spliced in with one of those connections.

-tested compression, all cylinders normal, 130, 130, 140, 140 (passed)
-tested fuel pressure, 33-38 psi (passed) (had gauge on backside of fuel rail)
-tested coolant temp sensor (passed)
-tested voltage to injectors from harness (all passed)
-tested fuel spray pattern from injectors (passed)
-tested coils resistances (both passed within spec, hot and cold)
-tested resistance of coil harness wires to ignition amp / motronic connector (passed)
-tested hall sensor via heat gun before start / installed known good one (passed)
-tested TPS for linear voltage from throttle closed to open (passed)

-Last recorded mileage: 46mpg, all highway miles, average speed of 80-85 ///////// 37mpg, combined highway and street


Things I have yet to do:

-balance the butterflies (they still look factory set based on the blue paint, didn't want to mess with them)

-somehow check the Motronic computer
---the motronic computer had stopped sending the ground signal to turn the cooling fan on (hence the switch for the fan on the dash), which makes me a little suspect of it as a cause for the misfire.

-replace the rubber connecting hose on the back of the TBs. (i've ordered this and will put it on when it gets here.






AGAIN: I believe bad / very dirty injectors were the main problem. As soon as I replaced these with new (reconditioned) Bosch type 2 injectors, the issue was VERY noticeably improved.  There was no more stuttering or dropping cylinders on clutch release.  It was still missing a little in the low RPM though.


Anyways, after I did all that, I took it to the BMW shop and had them set the TPS, CO pot, and air bypass screws as I don't have the right tools for that.  The current running state of the bike is pretty good, but I'm still looking in to replacing that last rubber piece on the back of the TBs, and I would also like to find a friend that would let me swap motronic computers to see if the issue persists.

I would start with the injectors before you mess with anything else.  Hope this helps.

Thanks for the update and (DOH!) my bike is an '84 K100 RS not '94!!
Will follow up on the injectors!
Also been reading about failing fans so I'll try and check that a) its free to turn, b) is coming in when its meant to.

I don't think the fan failing would be a cause of the misfire unless a) the engine is getting super hot, or b) the computer has internal issues causing the fan to not come on, which could possibly be a symptom of a bigger issue inside it causing the misfire.

NOTE: You're '84 k100 is a completely different system from my '92 k100.  Your bike uses L-jetronic fuel injection, and has a separate computer for ignition timing.  My '92 k100 uses Motronic fuel injection, and the ignition timing is part of the same computer.

This simply makes me think its more likely to be the injectors.  It could be other things, such as air bypass screw adjustments, mass air flow sensor, etc.

Point taken.

I don't use the bike everyday (meant to be something semi comfortable that my other half can join me on) but I will post back here when I do get around to looking at the issue and (hopefully!) improving things.

I was looking for a solution for my 'new' k100rs 1985, which had a problem almost identical to the one dealt with in this thread. First I changed all cracked rubber parts in the air and fuel system, and the fuel and air filter, but it didn't fix the problem.
Then I ran into the list of actions of Rabidchiwawa007, who said that his problem was largely solved by ultrasonic cleaning of the injectors. So I had my injectors cleaned too, but it didn't solve the problem a bit, although I do think it has a smoother start now.
Today I changed the ignition coils and spark plug wires, and that did solve the problem. It's like a got a new bike, all the stuttering is gone and the engine is a lot more 'drehfreudig' than it was.
Apparently the all black ignition coils of the early K100 aren't very reliable, but the ones on the later 8v editions (with a grayish brown color) are. So I bought a set of used coils from a 1989 K100RT (see picture), got on my bike and spent the rest of the day with a huge grin on my face , yihaa!

Hi Rabidchiwawa007,
First of all, thank you for all your extensive report on the issue of your k100, I've been learning a lot from it.
I've seen that this is already an old topic and that since 2013 there were no news or further developments from the search for your intermittent fault on your K100 16v, even though you were so close to finally find the faulty component.
I would love to know how it ended and what did you discovered!
I have a '96 K1100RS with exactly the same symptoms and now has reach the undrivable stage unfortunately.
I have already changed also, spark plugs, the fuel pressure regulator and I have tried the fuel thank from a faultless K1100LT and the problem was still there so with that I've excluded any possible fault from the fuel pump or filters.
I have also changed the HT spark plugs leads while a go, since I found the lead for the 2 cylinder was rotted.
I have ordered an Ignition Output Stage unit but now I am not sure if my K11 has that part since it is from April 96.
I really don't know what to do next and I am just guessing that by exclusion, maybe can be faulty coils when warm, or maybe a faulty Hall Efect Sensor, since disconnecting the plug from the TPS makes no difference and the problem remains exactly the same.
Though, a new set of Coils and a new HES can be very expensive so I would love to know a bit more before spending money, not knowing if the problem will be fixed.
I will be very thankful with all the available help since my bike is now undrivable.

m81a wrote:I really don't know what to do next and I am just guessing that by exclusion, maybe can be faulty coils when warm, or maybe a faulty Hall Efect Sensor, since disconnecting the plug from the TPS makes no difference and the problem remains exactly the same.
Though, a new set of Coils and a new HES can be very expensive so I would love to know a bit more before spending money, not knowing if the problem will be fixed.
I will be very thankful with all the available help since my bike is now undrivable.

Here is the post describing the solution to a problem similar to yours on a bike that is also similar to yours. It has a conclusion. The ignition switch was faulty; cleaning it helped get it back on the road. Consider taking it apart and inspecting it.

Also consider sending a personal message to Rabidchiwawa007 in case he hasn't been checking this site regularly.

Ivo9001 wrote:I was looking for a solution for my 'new' k100rs 1985, which had a problem almost identical to the one dealt with in this thread. First I changed all cracked rubber parts in the air and fuel system, and the fuel and air filter, but it didn't fix the problem.
Then I ran into the list of actions of Rabidchiwawa007, who said that his problem was largely solved by ultrasonic cleaning of the injectors. So I had my injectors cleaned too, but it didn't solve the problem a bit, although I do think it has a smoother start now.
Today I changed the ignition coils and spark plug wires, and that did solve the problem. It's like a got a new bike, all the stuttering is gone and the engine is a lot more 'drehfreudig' than it was.
Apparently the all black ignition coils of the early K100 aren't very reliable, but the ones on the later 8v editions (with a grayish brown color) are. So I bought a set of used coils from a 1989 K100RT (see picture), got on my bike and spent the rest of the day with a huge grin on my face , yihaa!

the ignition coils are very reliable ...after all they have in the most part lasted 25 years + of abuse and ignored attention to detail
its the lack of care and maintenance  that stuff the ignition coils up
 an open circuit on the high tension leads - ie plugtops - sparkplug connections  and leads to and from the coils can lead to a very high voltage ignition pulse which may  jump the coils internal winding creating a short circuit ...which will carbonise and form a fracture in the copper windings of the secondary ..(output ) windings .
the problem is self amplifying in as much as the as the coil gets more lossy ...the ignition voltage spike becomes higher in voltage but lower in current  to dissipate the energy ...creating more jump over issues within the coil ...and finally not enough to create a decent running spark .

everybody is aware to change oil ever 5000 to 10000  .but do they look at the ignition system  before issues arise  ? 

just food for thought