Hi guys

Having recently acquired a '90 K100RS, I have experienced an issue to which one of the members may have a simple solution.

The engine sometimes "stutters", almost as if fuel starvation or bad plugs. There is no fuel filter in the line to the injectors, and I have now realized that I need a 19 mm socket for the spark plugs (at least after this bike, I will have the full set - 16, 21 and now 19!), so I have not yet checked them.

I doubt however if the fuel starvation or bad spark is the issue here, as it does not occur only under acceleration. Sometimes, while cruising, or even when braking against the engine, I experience it. Under acceleration, I have kept the throttle open when this occurs, and after a second or two, the engine fires on all cylinders again (and then pulls like a tractor).

Could this be heat-attributed? I have noticed that the ignition leads are bunched up under the aesthetic spark-plug cover, and this condition seems to occur only once the bike has run for a while. (It is fairly warm down here now, around 30 deg C day temperature.)

could be leads

worth checking in any case

whilst your there test the secondary - or output of the coils as well ...should measure about 10 - 12 k  resistance
noteworthy is to look into the towers socket and see if they are clean

any greenish colour in one of the towers could point to the coil being open circuit or some seal -boot failure

leads typically should be within a few thousand ohms resistance end to end  comparatively for the same length of cable   so for number 1 should - could be about 3-4000,  2 maybe 2700,  3 could be about 2500, 4 about 2700 ....just as a guide not specific   but you get the idea of the differences ?

also look for rubber leaks in any of the induction path ...in particular the crankcase to engine breather tube located down near the coil packs to the plenum
in fact any rubber bits ...rubber ages and cracks

welcome aboard !!

HT leads or rubberware most likely.
You do know that the fuel filter lives inside the tank?
Another member had a baffling problem that was similar. Turned out to be some metal swarf around the hall effect triggers. They live behind the 'T' shaped cover on the front of the engine.

Also check the positioning of the Throttle position sensor, the PO may have played with it.

Exhaust valve clearances can also cause a stall if too tight... and they'll get tighter as the engines heats up. They're easy to check. Chris Harris has plenty of how-to videos on Youtube.

I seem to be harping on about batteries these days but just to rule it out, what condition is that in.... voltages? or get it tested at an auto battery shop. They'll do a load test.

Nothing more annoying than an intermitant stall.

If the engine is a 4 valve, exhaust clearances shouldn't be an issue.  I have heard from several sources, Chris Harris included, that the exhaust valves on the 4 valve engines don't close up over time like the earlier valves do.

Wouldn't hurt to check, but I don't think that is the problem.

Thanks for all the advice - great Forum!
I will tinker over the weekend, starting with the spark plugs, then ignition leads, also rinse the fuel tank and check the filter.
Comberjohn - I am an Electrical engineer, and thus familiar with the Hall Effect, but what exactly does it do on my K100? 

Big G wrote:Comberjohn - I am an Electrical engineer, and thus familiar with the Hall Effect, but what exactly does it do on my K100? 

Ignition timing.

OK, thanks Inge K
Makes sense, probably picks up the position of the crankshaft using the Hall Effect - clever!

Big G wrote:picks up the position of the crankshaft using the Hall Effect

Big G wrote:OK, thanks Inge K
Makes sense, probably picks up the position of the crankshaft using the Hall Effect - clever!

Got it in one. Happy St Patrick's Day Our beer normally goes green for today but black beer is much better than no beer 

Thanks for all the advice guys - lots of tips and tricks on this forum!

I found two spark plugs without barrel nipples, and fitted one of them, the other had a barrel nipple stuck in the plug cap, which was quite a mission to get out. 
This went a long way to smoother running, but I found there was still a spark breakdown after some high-speed cruising, seemingly when the engine gets hot.

I have now replaced the DR8EA's which I bought the bike with, with DR7EA's, and it is even better, but still develops a slight flat spot when hot. 
We are now in Autumn down South here, with daytime temperatures in the mid to high 20's, but when summer comes again, I'll be driving in temps around mid to high 30's (deg C).

Next step is the HT leads, as it seems the ones on the bike are the OEM leads, circa 1990, with 78000km worth of duty.

I have read a lot about aftermarket leads, as the OEM BMW leads are the price of a whole bike (almost). I believe there should be some resistance in the circuit, else one can damage the coils?

My question: Can I fit standard leads together with the DR7EA's, and (b): How important is it for the leads to be the same length for all four cylinders?

Try RealmEngineering.com in the U.K. 
Along with a specially designed rear suspension unit for the brick, they also do a set of Ram ignition leads for it.
About half the price of original and seem to be top quality.
I'm sure others can vouch for that.

If you have stock coils and stock leads the plugs should not be R rated. D7EA or D8EA will work, not DR7EA or DR8EA. The plug leads incorporate the resistors. Aftermarket leads may not and then you need the DR plugs. They don't come with the screw on bobbins on them so mind the old ones carefully.

Everywhere I go here I end up with D8EA, even the local BMW guys puts them in. Book says D7EA. I get the D7EA very cheap but I have also had them fail shortly after installing them so don't dismiss plug problems even if they are new. Find the cooler exhaust header pipe and swap the plug before going in deeper.

For the cost of the D7EA plugs its worth trying them to see if it solves the problem.

Hi Olaf
So that's the story with the resistors  - Tx.
What do you mean:
Find the cooler pipe ?
Cheers,

Big G wrote:Hi Olaf
So that's the story with the resistors  - Tx.
What do you mean:
Find the cooler pipe ?
Cheers,

Took me a minute or five to work out what I wrote, wasn't at all clear. What I meant was the dud cylinder will not warm up as quick so the exhaust header will be cooler. Or just put in a set of D7 or D8EA plugs and see what happens, they are  a lot cheaper than new leads of any kind. The K will run on either.

Big G wrote:......
So that's the story with the resistors  - Tx.

The standard leads have resistance built in so you don't need the resistor SPs, just the D7EA or D8EA, 8 being a cooler plug. The book says 7 but some owners use 8 with good effect.

HT leads should measure around 5k ohm end to end.
You can buy new ones from here pretty cheaply.
http://www.euromotoelectrics.com/Ignition-Wire-Set-BMW-K100-BMW-WSK100-p/bmw-wsk100.htm

KH

They look good but how do you get them off the plugs? The original caps have a metal tab for pulling them off easily.

They are NGK caps and come off very easily, you also don't need the little bobbins.

Hey Olaf
I've not used them, just bookmarked them for reference for when I need replacement.
I have thought that myself but they say they're for the K100. From the diagram, it looks like the SP terminal nut connects less than half way up inside the NKG cap leaving the rest to protrude out further. On the BMW SP cap the terminal nut fits nearly all the way up inside the cap hence the tab to be able to get a hold on them.
The NKG cap also has an angle so that may make it easier to remove as well.
I'm sure they'd work but might be worth checking with them first
There ya go... Rick can confirm

92KK 84WW Olaf wrote:If you have stock coils and stock leads the plugs should not be R rated. D7EA or D8EA will work, not DR7EA or DR8EA. The plug leads incorporate the resistors. Aftermarket leads may not and then you need the DR plugs.

Bad advice, Olaf.  I am pretty sure that the 4 valve K100RS uses resistor plugs.  The BMW parts fiche calls out XR5DC for that engine.  The earlier K engines used non-resistor plugs, but not the 4 valve RS or the 1100.  Using the D7EA will burn up the coils.

I am presently running NGK DR7EA plugs after replacing the fouled DR8EA's my '92 K100RS came with.  It looks to me like unless you are running a lot of high speed slab, the cooler DR8EA's will have a bit of trouble staying as clean as the 7's.

Hey Point Seven Five

Hands up on my part. Guilty as charged, never checked on 8 valve or 16 valve engine.

I took it to be 8 valve. My Clymer gives this for K100RS with a change from X5DC to XR5DC from 91, presumably for the Motronic unit 16 valve.

The link to the plug leads was also for the 8 valve, with a different link for the 90-92 K100RS directed to K1100RS.

Does this mean the change was for 91 model year?

Either way your advice is correct for 16 valve.

Olaf.

I've had 2 K100RS 16v's and they are a bit grey in respect of specification I've found-especially in the wiring dept.

However,I had this self same problem on my June '90 16v and I cured it by keeping plenty of fuel in the tank.
When I accelerated,all the fuel would move to the back of the tank leaving the fuel pump and therefore fuel supply with nothing around the pump base causing the bike cut temporarily. Everything inside the tank was stock.
Interestingly,the August '91 16v doesn't have that problem but tank internals seem the same.

 Does the bike cut with a full tank? It may seem like a daft question but worth asking-sorry if it seems really obvious.

Olaf, No problemo!  It's something you wouldn't notice unless you owned one and bought the wrong plugs.  Please, don't ask me how I know.

Point-Seven-five wrote:

92KK 84WW Olaf wrote:If you have stock coils and stock leads the plugs should not be R rated. D7EA or D8EA will work, not DR7EA or DR8EA. The plug leads incorporate the resistors. Aftermarket leads may not and then you need the DR plugs.

Bad advice, Olaf.  I am pretty sure that the 4 valve K100RS uses resistor plugs.  The BMW parts fiche calls out XR5DC for that engine.  The earlier K engines used non-resistor plugs, but not the 4 valve RS or the 1100.  Using the D7EA will burn up the coils.

I am presently running NGK DR7EA plugs after replacing the fouled DR8EA's my '92 K100RS came with.  It looks to me like unless you are running a lot of high speed slab, the cooler DR8EA's will have a bit of trouble staying as clean as the 7's.

...

wrong !!

it will provide a higher and longer spark energy  ...which when running a lower stoichiometric fuel ration ( like they designed into ignition system for leaner running at cruising speeds on the 16 valve units ) will present as a lean burn at the plug as the plug will burn at a higher temperature

it should not affect the coils at all ...given that they are running resistive leads .  

the resistive plugs could be considered as a match for the fuel mix provided by the system and lower emi rfi (radio interference ) as demanded by governments at the time for compliance ..
the coils primaries are lower than the 8 valve units to produce a  higher and shorter peak voltage spike for ignition through the added resistive loads to the plug tip .

Point-Seven-five wrote:Olaf, No problemo!  It's something you wouldn't notice unless you owned one and bought the wrong plugs.  Please, don't ask me how I know.

More annoyed with myself for simply assuming the 8 valve rather than 16 valve motor. I suppose that's why we try to put info in our footers, so we don't put our foot in it.

I have stuck with the D8EA instead of D7EA simply because they come out the right colour but I regularly get a 320 mile round trip motorway run so I figure err on the side of safety. Ever since I got bikes I always stayed on the side of slightly cooler and never had problems.

A bottle of STP in the tank might help clean the injectors http://www.stp.com

92KK 84WW Olaf wrote:Hey Point Seven Five

Hands up on my part. Guilty as charged, never checked on 8 valve or 16 valve engine.

I took it to be 8 valve. My Clymer gives this for K100RS with a change from X5DC to XR5DC from 91, presumably for the Motronic unit 16 valve.

I put my hands up too . Should've read the original post again but here's a good case for placing the Model AND Vin Number into the signature ... just sayin'... says me who hasn't done that yet.

According to realoem.com the 4V (production code 0523) started in 03/1989 and had resistor SPs XR5DC
And the 2V (Production Code: 0503) finished in 10/1989.
I've put a separate post up about this for discussion so as not to hijack this thread

Here's an interesting link about spark plugs from NKG which should be required reading.

could it be the fact that the gap presented by the fouled plug discharges at an earlier ( breakover voltage but more like leakage ) but letting some gap between the two devices ...the energy will not jump the gap until it builds to a sufficient  voltage - energy capable of clearing the low resistance carbon track on the misfiring plug ?

just what makes sense to me rawdon

hope that helps for another viewpoint

Hope you folks don't mind, but just a couple cents worth of random pedantic musings on the subject...

When a plug finally accumulates enough carbon to bypass the electrode gap the ultimate voltage will be very low as the carbon has virtually no resistance to the flow of current compared to the air gap between the electrodes.  The plug will not create a spark.

The spark itself is generated by the collapse of the magnetic field generated by the primary windings of the ignition coil. This collapse is triggered by the ignition system shutting off the power to the coil.  This collapsing field generates a small bit of electrical current in the secondary winding that wants desperately to flow to ground/earth.  As long as the current doesn't flow, the voltage will rise, into the 1000's of volts, until there is enough voltage to allow the current to jump the gap in the plug. 

A dirty plug essentially has two resistors in parallel providing the current a path to ground.  The carbon, and the air gap.  Even if the plug is still providing a spark, there will be a very small amount of electrical energy "stolen" by the carbon, which will slightly reduce the heat of the spark.  This continues until all the energy is passed through the carbon and the plug doesn't "fire". 

A wider throttle opening allows more air into the cylinder on the intake stroke and consequently results in a higher pressure in the cylinder at top dead center of the compression stroke.   At higher air pressures in the cylinder the plug will require a higher voltage to generate a spark.  A dirty plug will have trouble sparking at high cylinder pressure because the small amount of current bleed through the carbon is preventing the build up to the higher voltage necessary.  This will result in situations where accelerating at small throttle opening does not have the misfire that occurs when the throttle is opened fully.

A cooler plug will accumulate carbon at idle and low speed.  This can in some cases result in a stumble or lag on acceleration.  This carbon will quickly burn off after a few seconds of high speed running.  This is why tuners will do at least two plug readings, one at full throttle and one at idle. 

I am not sure if you are saying that the fouling affects the timing, but in my experience, the answer is no.  The build up of the secondary voltage is essentially instantaneous.  Where the problem comes in is when the carbon is at that point where there is enough to start burning on the plug's nose from the combustion heat of the fuel.  This is the ignition source that causes preignition and detonation.

Heat range is a tool you can use if you understand it.  I have a 4 cylinder marine engine on my sailboat that has a fouling problem on one of the cylinders.  This cylinder is at the point where the cooling water enters the block, and the head stays a bit cooler there compared to the other cylinders.  This cylinder also has an issue with a stuck oil control ring so a bit of oil is getting into the cylinder making things a tiny bit richer.  Plug readings at idle pointed out the problem.  Since I didn't want to bother pulling the engine to do a ring job on a single cylinder on an otherwise tight engine, I simply went one heat range hotter on that cylinder.  Fouling problem solved.  The engine runs great.

AC(as in AC spark plugs) are the initials of Albert Champion, the founder of the Champion Spark Plug Co. and the AC Spark Plug Co.

A cooler plug will accumulate carbon at idle and low speed.  This can in some cases result in a stumble or lag on acceleration.  This carbon will quickly burn off after a few seconds of high speed running.

We used to refer to that as an Italian tune up.

Wonder is there a way of unsticking the stuck piston ring? Acetone or something like that left to soak through? Just a thought.

Again, a thorough explanation of a sometimes tricky subject from Point-seven-five.

This man is worth reading/listening to.  

Bill

92KK 84WW Olaf wrote:A cooler plug will accumulate carbon at idle and low speed.  This can in some cases result in a stumble or lag on acceleration.  This carbon will quickly burn off after a few seconds of high speed running.

We used to refer to that as an Italian tune up.

Wonder is there a way of unsticking the stuck piston ring? Acetone or something like that left to soak through? Just a thought.

Or use anti-fouling?

92KK 84WW Olaf wrote:A cooler plug will accumulate carbon at idle and low speed.  This can in some cases result in a stumble or lag on acceleration.  This carbon will quickly burn off after a few seconds of high speed running.

We used to refer to that as an Italian tune up.

Wonder is there a way of unsticking the stuck piston ring? Acetone or something like that left to soak through? Just a thought.

Trouble is, a little bit of low rpm running puts the carbon right back.  I only mention it as a tip to anyone running a cooler heat range plug.  If you are running the correct heat range, it means you need to check the mixture or the engine temperature.

I have tried the "solvent rebuild" with no luck.  Problem may also be a loose valve guide.  Engine is 40+ years old.  The hotter plug has got the job done as far as my needs.  Engine runs well on all cylinders now where previously number 4 was always dropping out.  Life is too short and I don't run the engine enough to justify doing much more to it.

92KK 84WW Olaf wrote:Hey Point Seven Five

Hands up on my part. Guilty as charged, never checked on 8 valve or 16 valve engine.

I took it to be 8 valve. My Clymer gives this for K100RS with a change from X5DC to XR5DC from 91, presumably for the Motronic unit 16 valve.

The link to the plug leads was also for the 8 valve, with a different link for the 90-92 K100RS directed to K1100RS.

Does this mean the change was for 91 model year?

Either way your advice is correct for 16 valve.

Olaf.

Morning .75 & Olaf

I have now been running the D7EA's for a couple of weeks, and the flat spot is gone. However, I suspect it may have been mostly due to the old plug barrel nipple stuck in No.3 arrestor cap. I eventually managed to extract it and with the new nipple on the plug, the fit is nice and snug - no throwaway spark anymore!

Also, I use my steed mostly for commuting - stuck in 2nd/3rd gear traffic most of the way at low engine speed, but get the opportunity for a nice high speed run on the motorway for about 5 km (my every morning "jollies"). I reckon I will thus stick to the hotter 7EA's.

Now I just need to clarify: to "R" or not?
My bike is the K100RS 16v 1990 model, VIN: 6408293K100RSCJ; Engine No: 104EB17902194.
Should I be running D7EA or DR7EA?

Cheers,

just check the colour of the plugs

that will tell more than any manual .....if it suits your driving regime and choice of fuel , why change ?

might be a different story if sitting up high in the revs for many miles though ..like on holidays and a good run on the highways for a week or two

or changing fuel standards  ie 98 instead of 91 octane

done well !

Thanks Charlie
Colour is good with the 7EA's, I will stick with them - just worried about the resistor or not.

Use a DR7EA it is a resistive plug and will give you a better spark. The resistive plug is needed to match the impedance of the coil secondary windings to the plug and leads, if you don't use the resistive plug you stand a chance of damaging the output stages of the ignition electronics.

Hi Rick
Thanks for the advice - just some feedback:
I have changed back to DR7EA, but now am again suffering from spark breakdown.
I suspect the ignition leads are shot - they are the originals from 1990, with 80 000 km on them.
I am going to search the site for advice on replacement leads, as the originals are going to set me back around ZAR 3 500.
However, rather that than having to buy new coils!

hi ...check the ram shock site 

they have a good price for leads ...well made,

[url=http://www.realmengineering.com/ram power leads.html]http://www.realmengineering.com/ram%20power%20leads.html[/url]

Big G wrote:Hi Rick
Thanks for the advice - just some feedback:
I have changed back to DR7EA, but now am again suffering from spark breakdown.
I suspect the ignition leads are shot - they are the originals from 1990, with 80 000 km on them.
I am going to search the site for advice on replacement leads, as the originals are going to set me back around ZAR 3 500.
However, rather that than having to buy new coils!

Going back to the original confusion over 8 and 16 valve engines, is it possible your 1990 leads are off an 8 valve engine? My 92LT is 8 valve and they were still in production. If these were put into yours at some point.......then they should be mixed with plugs without the R rating. The 8 valve uses resistive plug leads and mixing these with a resistive plug may weaken the spark too much. If they are off the 8 valve maybe the solution is stay with the D7EA plugs and not bother changing the leads.

I stuck with the D8EA because a lot of my miles are motorway so they get cleaned out pretty well on a regular basis. I don't have a traffic commute as my office is based at home.