1985 BMW K100 random miss

[warmas]

Group:
I have read with interest many posts here re: Kbike repairs.
I have attempted to breathe new life into mine after spotting it for sale along the roadside. Apparently noone before me, as usual, was foolish enough to buy it, but I have been able to make it run, rather well, and all systems on it function, at least for now, properly.
Except, the motor has a randon miss or ignition cut-out noticeable at low rpm-no load power settings. It is quite noticeable at idle or when practising low speed sharp turns: the hesitation makes balance more difficult. The miss is not noticeable under full throttle acceleration. The green neutral light seems to blink in time with the miss. The blink is noticeable at idle.  I have studied the wiring diagram for this bike. The power for the neutral light is supplied through fuse #1 from the emergency kill switch, the power to the coils  from the emergency kill switch is not fused . I think the miss is electrical in nature; the fuel supply system seems in order. It seems a loose connection, in either the supply or ground circuit to the coils/neutral light could cause the miss.
Separately, the bike does not want to start when cold. A shot of starting fluid to the air intake causes it to start immediately.
Choke control seems to operate, but engine is hard to start cold. Fan for radiator comes on to prevent boiling over, so I suppose coolant temp sensor works OK. I have not tested it with thermometer/ohm meter.
Plugs, injectors, coils, connections to them appear sound: no sparks in the dark, interrupting electric signal to each injector causes a noticeable change in engine rpm.
I disassembled, contact cleanered, and reassembled emergency kill switch, unplugged and contact cleanered and plugged in eletronic fuel injection controller. No change.
Have not tackled ignition switch yet.
I am most interested in any and all ideas, comments, suggestions, etc. you may have.
This bike is considerably peppier than the R100 I have, but does not yet run as well. It rides nicely, although it sounds like it should be powering a hydraulic pump or air conditioner. It is more difficult to troubleshoot.
Thanks in advance.


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[warmas]

Group:
I have read with interest many posts here re: Kbike repairs.
I have attempted to breathe new life into mine after spotting it for sale along the roadside. Apparently noone before me, as usual, was foolish enough to buy it, but I have been able to make it run, rather well, and all systems on it function, at least for now, properly.
Except, the motor has a randon miss or ignition cut-out noticeable at low rpm-no load power settings. It is quite noticeable at idle or when practising low speed sharp turns: the hesitation makes balance more difficult. The miss is not noticeable under full throttle acceleration. The green neutral light seems to blink in time with the miss. The blink is noticeable at idle.  I have studied the wiring diagram for this bike. The power for the neutral light is supplied through fuse #1 from the emergency kill switch, the power to the coils  from the emergency kill switch is not fused . I think the miss is electrical in nature; the fuel supply system seems in order. It seems a loose connection, in either the supply or ground circuit to the coils/neutral light could cause the miss.
Separately, the bike does not want to start when cold. A shot of starting fluid to the air intake causes it to start immediately.
Choke control seems to operate, but engine is hard to start cold. Fan for radiator comes on to prevent boiling over, so I suppose coolant temp sensor works OK. I have not tested it with thermometer/ohm meter.
Plugs, injectors, coils, connections to them appear sound: no sparks in the dark, interrupting electric signal to each injector causes a noticeable change in engine rpm.
I disassembled, contact cleanered, and reassembled emergency kill switch, unplugged and contact cleanered and plugged in eletronic fuel injection controller. No change.
Have not tackled ignition switch yet.
I am most interested in any and all ideas, comments, suggestions, etc. you may have.
This bike is considerably peppier than the R100 I have, but does not yet run as well. It rides nicely, although it sounds like it should be powering a hydraulic pump or air conditioner. It is more difficult to troubleshoot.
Thanks in advance.

[warmas]

Thanks for the greeting.
I have no clue how to do that.

[warmas]

If I knew how to record and post audio and video of the miss I would. Figurring out this miss is about all I can do.
I give up: what caused his miss?

[Laitch]

Thanks for the greeting.
I have no clue how to do that.

Record the sound using your phone. Upload the sound file to the site following the video/audio instructions within the Photo Guidance section in the Welcome to Motobrick section.

[warmas]

thanks for the pointer, will do asap.

[The Mighty Gryphon]

Clean every connector and switch with DeOxit electronics cleaner.  It's one of the most important jobs that needs to be done to any old K bike when you buy it.  Other electrical stuff that needs to be cleaned up is the starter commutator and all the ground connections on the transmission and the frame backbone.

[Laitch]

Many members with engine performance problems have recorded the conditions using their phones to make videos with sound, then have created YouTube accounts. After uploading the video files to YouTube, they post the links here. After that, we all gather around the patients using our personal incantations, ritual dances, incense burning and experience to diagnose the source of the problems.

Try that, but keep cleaning all the connectors as Gryph has recommended while deliberations continue.

[warmas]

I disassembled, inspected, contact cleanered and reassembled the ignition switch. It did not need opened and cleaned.
Contact cleanered all connectors beneath tank, and the few in the relay box. Did not unmount relays and contact cleaner them as I had reseated them on their bases early September.
Unplugged coolant temp sensor,  resulting fuel mixture then too rich for idle.I think the coolant temp sensor is working properly, as fan also turns on and off. Depressing start button after engine is idling raises rpm 1-200, engine apparently is running lean at idle. Depressing start button at a warmed up 2k rpm raises rpm to 2.8k approx. Such a rise says the engine is running lean.Started right up but does not want to idle until it has warmed up a bit.
Bike runs no different, has very annoying miss/hesitation. Under full throttle acceleration no miss or hesitation is noticeable, probably a richer mixture provided by fuel injection computer.
Pulling the various injector leads one at a time causes, sometimes, varying rpm changes. Disabling injector #2, for example, sometimes results in 1k rpm drop, sometimes 400 rpm drop. I ran the bike on the center stand at 3k rpm in the dark for these injector tests. With all four cylinders on line, all four exhaust pipes were a dull red orange color. I guess each cylinder is making similar power, judging by those colors.
Am going to balance throttle bodies and check injector fuel spray patterns, Have never done either to this bike.
Balancing the carbs on the R100 resulted in  much smoother engine operation. The idle mixture for that bike is specified to be leaned to max rpm at idle speed and then enrichened a bit. My K100 appears to be running on the lean side of peak rpm at low power settings, and I have seen lean mixtures cause rough engine operation. I wonder how the fuel mixture can be richened at low power settings for a 1985 K100.
Your thoughts?

[Laitch]

Your thoughts?

I'd like you to divide your text into paragraphs to make your thoughts easier to read.

After electrical connector clean up, an old bike like yours needs a tuneup. You need to be certain the air filter isn't clogged. You need to replace the fuel filter if you don't know its age. You need to inspect the fuel tank's interior and clean it if it needs it. You need to check the condition of the fuel tank hoses and determine if their connections are tight. You need to clean and tighten the battery's ground connection on the transmission and the connections on its post terminals.

You need to check the valve clearances right now—something you haven't described as part of your program. Maybe you assume that we understand balancing throttle bodies means you'll also check the valve clearances. Don't assume anything. You should also check the throttle body manifolds (bushings) for leaks and the crankcase breather hose for integrity before you perform the balance procedure.

Don't go at this thing piecemeal, hunting here and there for a solution like almost every starstruck new K owner here seems to do. Get it set to spec then see what happens.

[johnny]

greetings...

i gottsa 1 thought... post up a video with audio...

brunhilda baywerische-motosenwerken will be back from her battery of blood transfusions soon...

that should be enough said...

j o

[The Mighty Gryphon]

Have you taken a plug reading after letting the engine idle for 15 minutes?  That will tell you a bit about the mixture without arsing about with the injectors.

Definitely do a very careful inspection of the bushings above and below the throttle bodies and especially the zigzag hose from the crankcase to the airbox.  That hose is famous for cracking and causing air leaks and mixture problems.  If you haven't checked it already, I am willing to bet that you will find that it's cracked near the hose clamps.

Last, there are two separate temperature sensors in the engine temperature sensor body.  One controls the fan and the other controls the mixture.  Just because the fan works, it doesn't mean the mixture signal is correct.  Not only could the sensor be whack, but the cable could be worn through and shorting to ground, making the ECU think the engine is warmer than it really is.

[Martin]

The 2v Bricks have built in diagnostics for mixture strength. Set the idle to 1000 RPM or slightly more (under 1000RPM the test won't work), then press the green starter button the idle should stay the same or rise slightly. If it rises significantly the mixture is lean, if it drops significantly or dies the mixture is too rich.
Regards Martin.

[warmas]

     Thanks to all for the comments

[warmas]

     Thanks to all for the comments.
My inspections cause me to believe the ignition system to be in good order.

I have recently checked the air filter, it is of unknown age but is in good condition.

Fuel filter, pump, tank, wiring, connector, circuit, hoses are, based on my recent inspections, repairs, and replacements, serviceable. I have not measured fuel pressure. I have not inspected the injectors.

Since I forgot yesterday to check, clean and tighten ground connections, those are on my list of today's tasks.

The bushings and clamps connecting plenum to throttle bodies have been inspected by me repeatedly and appear serviceable. I have not tested them for low manifold pressure leaks. Will do soon.

I have not yet checked valve clearances, and don't yet know how to change them. Valves are quiet.

I have checked the plugs several times, but not yet after a strictly idle-rpm run. At my checks they have been white to very light tan. Will do.

The crankcase-to-airbox vent port in airbox is plugged, and vent line is open to atmosphere through a small filter. Port plug bears closer inspection.

Re: coolant temp sensor, my suspicions precisely. My experiment by unplugging it and noting change to very excessively rich mixture and reconnecting it and noting mixture as before and, separately, the fan cycling with temperature are the support for my conclusion as to it's proper operation. I could be wrong. I think the change in resistance with temperature is a signal delivered by the sensor. I have not measured this change with an ohmmeter.

I have, as noted, depressed the starter button at a few different rpms and always noted an increase in rpm, a few hundred at idle to several hundred at above 2k. These changes say to me the mixture is lean. I presume pressing the start button while the engine is running somehow richens the mixture?

Thanks again for the helpful suggestions and ideas. My experience has shown me repeated careful attention to detail usually reveals unfounded assumptions. Murphy's Law.

[The Mighty Gryphon]

Your plug readings confirm a lean mixture at running speeds, I suspect you will see that at idle as well.

I can't say why, but I would replace the crankcase breather tube ASAP, mainly for peace of mind.

The temperature sensor has a negative coefficient so the resistance gets lower as the temperature rises.  2500 ohms at room temp, and about 250 ohms when warmed up to normal operating temperature.

Another thing to check is the MAF.  They have been known to go bad.  I have not had to troubleshoot one, but I am pretty sure there are threads here and at other sites giving info on checking it.  The good news is that if you need one, there are a few of them out there.  It's possible that the flapper is not closing properly, or the complex resistance element has worn spots and is not making contact with the wiper.

You could also have plugged injectors.  Have you run any Techron through the engine?  It is a nearly magic elixir for old bricks and clears up a lot of problems caused by stale fuel.  A bike that hasn't been run for a while should have at least a couple tanks with Techron run through it.

Quiet valves are scary on these bikes.  It means they are probably tight, and can result in burned exhaust valves.  Check them ASAP.  There are threads here on how to adjust them and the tools you will need.  There is a source for reasonably priced shims:

https://www.newmotorcycleparts.net/motor_parts/valve_shims.html

[Laitch]

I have not yet checked valve clearances, and don't yet know how to change them. Valves are quiet.

To support Gryph's observations, clearly you aren't up to speed when it comes to valve and tuneup knowledge. Just because you don't yet know how to check valve clearances or adjust them doesn't place the procedures in a lower rank on the work list priority. This procedure should be near the top after checking air, electrical, and ignition status. Checking and adjusting valves is essential to tuning up the engine.

Quiet valves can be valves with excessively tight clearances. Tight valves can cause loss of compression, loss of the valve seats, breakage of the valves themselves and severe damage to an engine if any of those broken parts are pounded by the piston. Exhaust valves with tight clearances are quiet but can cause noisy damage more frequently than intake valves. Clearances set to spec are essential for a properly running engine. Symptoms of problems can appear gradually but the cost of ignoring them can be significant. It's ok if valves tick slightly.

 Plenty of instruction on checking an setting valve clearances is available on the  site.

[warmas]

Thanks again.

I will compare the CTS resistance readings against those posted.

The crankcase breather tube replacement is one of my many tasks.

The MAF sensor and flapper will require research by me to troubleshoot.

I have burnt some Brand X fuel system cleaner during the few hundred miles I have ridden this bike.

I am aware of the consequences of quiet valves. More research is in order. Thanks for the tip re: valve shims. I have never adjusted a valve with shims.

I am looking forward to the results of this troubleshooting exercise, and grateful of the advice available here.

[The Mighty Gryphon]

Don't give up, and keep us posted.  This bike is worth the effort.

[warmas]

Checked valve clearances today, all were within tolerance.

Sprayed starting fluid at intake manifold at cylinder head, caused rapid rise in rpm.
Perhaps I have found what is causing the rough running at low power.

Separately, fuel pump quit, engine died. Verified pump connector plugged in, pump didn't function. Half an hour later, started up as usual. More food for thought.

Administrator wants me to post video with sound, I will have to learn how.

[The Mighty Gryphon]

That's the thing with the tank connector, even when it's plugged in, it doesn't work.  You need to have it make better contact between the pins and sockets.  In the worst case scenario you need to replace it with a better connector.

You might have cooked o-rings at the base of the throttle body bushings.

[johnny]

greetings...

does it miss while on the center stand when the engine is running...

j o

[Laitch]

Sprayed starting fluid at intake manifold at cylinder head, caused rapid rise in rpm.
Perhaps I have found what is causing the rough running at low power.

That's right. You have found one source of rough running. Now carefully spray each manifold bushing to determine if there is more than one defective bushing.

[warmas]

Thanks for the clemency, I repent of my sins. Indulgences forthcoming.

[Laitch]

Thanks for the clemency, I repent of my sins. Indulgences forthcoming.

Thank j o and Acute Toxicity. I'm just a prophet without honor in his own land. :oldguy: