Hi, I am having trouble with my 86 k100. Hard start, rough running , white smoke, ect. 
I have tried all the stuff. Today I just tested the tem. sensor, # 10 pin and ground and got 2.14 ohms. Tested the coils on the spark plug sockets and got 9.76 k ohm.
How do those numbers sound ?
For some reason its 1 and 4 cylinders that seem to be hard to fire.

White smoke can be the coolant leaking into the combustion chamber and those numbers are OK if the engine is at ambient temperature.

yankeeone wrote:Hi, I am having trouble with my 86 k100. Hard start, rough running , white smoke, ect. 
I have tried all the stuff. Today I just tested the tem. sensor, # 10 pin and ground and got 2.14 ohms. Tested the coils on the spark plug sockets and got 9.76 k ohm.
How do those numbers sound ?
For some reason its 1 and 4 cylinders that seem to be hard to fire.

2.14 ohms ?....I hope you mean 2.14 k ohms ...and I hope the engine was cold when you took the measurement

at 2.14 ohms the fan should have been running for quite some time .... as it triggers the temp - fan relay  at about 100 ohms 

usually we measure the resistance to the temp sensor at the under seat ecu on pins 10 and 13 ....can make a difference , as this is what this ecu sees ...rather than a faulty path to ground , which is quite common ,,,and one of the faults with the temp sensor (corrosion between the temp sensor and the water stub housing ---in the threads , caused by dissimilar metals and the stuff in the radiator system creating a bad earth path )

don't forget that on all the early 2 valve k bikes  the temp sensor that controls the ecu is a double sensor within  the same device , the third contact is the water stub earth path .

Thanks guys, what should I expect to get for readings on the ecu connector on pins 10 and 13?
It seems most of the problem is on 1 and 4  , the exhaust pipe are cold , and when I can finally get some rps going they are cooler than 2 and 3.

First of all, if it was the temperature sender, ALL the cylinders would be giving you trouble.

Second, early K100 coils have a reputation for failing.  I suspect you have a bad one.  It may not be a bad idea to replace the coils with the later version. 

A test might be to swap your coils and see if the problem moves to the other cylinders.

yankeeone wrote:I am having trouble with my 86 k100. Hard start, rough running , white smoke, ect. 
I have tried all the stuff.

Which stuff is that—Ambien, Excedrin, Cialis, Ecstasy? .75's coil swap seems sensible; a compression test might be useful, too.

Stuff/
Switched computer under the seat with known working one
switched control unit under the tank with known working one
hall unit
valve check 
compression test 
switched coils with known working coils
tested fuel pump pressure
plug wires are new
do have spark on 1 and 4
switched air flow meter with known working one
removed injector rack and checked for fuel from injectors
checked for vacuum leaks
checked breather hose

Point seven five, I agree with your assessment. I did swap coils ,but no help.

The bike was running great. Just rolling along at seventy five, then sudden loss of power.
When trying to start now, early cranking ,trying to start leaves 1 and 4 exhaust pipes cold, If can get some rpms up then they get hotter. but not as hot as 2 and 3

Check the wiring to the coils.
Regards Martin.

Another easy check on the coil and leads is to remove  the coil cover and the spark plug cover plate and run the bike at night in the dark  and hopefully you don't see any blue  dancing lights

or in this case hopefully you WILL see dancing sparks ,  enough to be able to identify issues

I might add , a set of  coils off a working bike  , doesn't mean that they are good in all respects , had a set recently that idles ok , with a struggle ...but broke down on acceleration and higher revs - only .....

removing the coil cover let me hear the jumping over of the high energy spark and identify the bad one , im as blind as a bat anyhow ...smile

Thanks, I will try running the bike in the dark, it just got dark here. 
I think I will try a test for continuity on the harness side of hall sensor and coils.

Solved --  spark plugs, particularly number one , they only have about 5 thousand miles on them , so looks like a failing coil as well.
Thanks for your help

Anyone mentioning problems, 1 and 4 are on one coil, 2 and 3 on the other. Anything affecting 1/4 together or 2/3 together its most likely to be coil or coil wiring related. Swap coils and see if it changes with them. If it does then its coil. If not then its coil wiring which can include one of the two Hall sensors.

yankeeone wrote:Solved --  spark plugs, particularly number one , they only have about 5 thousand miles on them , so looks like a failing coil as well.
Thanks for your help

What did you see???  What is wrong with the spark plugs?  What was the coil doing??  I thought you swapped coils and the problem stayed on cylinders 1&4.

Like a lot of things that go wrong, it seems to be a series of little things that add up. 
I am thinking that due to a weak coil the plugs took on a lot of carbon, I did change coils but with one that was 
probably not much better, so it couldn't overcome the carbon plugs. 
I did test the spark on number one cylinder early on and when it was out it did spark , and they didn't seem 
bad visually, but apparently they were. 

 I will get new coils.

What spark plugs have you? Do they have bobbins on them or do they show a threaded top?

Point-Seven-five wrote:First of all, if it was the temperature sender, ALL the cylinders would be giving you trouble.

Second, early K100 coils have a reputation for failing.  I suspect you have a bad one.  It may not be a bad idea to replace the coils with the later version. 

A test might be to swap your coils and see if the problem moves to the other cylinders.

This was the one to follow as an early test.

Hi, Installed updated version of the coil. Runs great. I think a weak coil allowed the plugs to foul. when I put in new plugs she ran, and now with new coil she runs better then ever. 
It seems I will need new bigger screws for the cover and a little shimming of the coil spacing to get the old coil cover to work.
I bought the coil from Bobs BMW ,good price and got it in two days.Now I need to get another one for # 2 and 3

 Now I can continue on with the RT to RS conversion and repaint.

that's a good result so far
good luck with the rest of it

Thanks for the update.  Those early coils have caused a fair number of headaches.

It has some clean connections now too!

You discovered something I discovered.....to get the coil cover to fit you need either two old coils or two new type coils.....I found it doesn't fit if you mix the two types...I have both coil and cover types here. I needed to replace the coils in my new 83 RS and put one new one in...cover would not fit so I swapped the second one as well since I had them.