I have a 1985 BMW KRT100 and have had this problem for over a year now.  it has to do with warm up and idle speed.  

When the engine is cold it will start up no problem using the fuel enrichment lever.  It appears to idle Ok for a brief period, then it conks out and will not start again.  If I leave it alone for about a minute, it will start back up again and appear normal.  It may do this once or twice, but after the engine begins to warm up fully, the problem is gone.  After that, even if the bike sits for an hour or so, as long as the motor is still warm, it will start up and act normal.  I have changed the coolant temperature sensor but no difference.  Also have checked Z tube and rubber parts for air leaks, but found none.  

The other problem is with idle.  After warm up, when I pull up to a stop light the engine will stall normally.  Not always though!  I turned idle speed up and it didnt help.  I have looked for leaks using a propane torch unlit around rubber connectors but found no increase in idle speed.  Any ideas on these problems?  When warmed up the bike runs ok, I dont notice any major issues other than what was mentioned already.

I've had similar symptoms where the problem turned out to be bad coils, check them out. This is more likely if yours is the earlier model, there was a model change in 1985.

daveyson wrote:I've had similar symptoms where the problem turned out to be bad coils, check them out. This is more likely if yours is the earlier model, there was a model change in 1985.

Interesting, did you have both idling and warm up problems?  Is there a way to check by my VIN whether this is an early model?  The history of this bike is that it was purchased in West Germany by a GI and brought back to the US.   The key on it said made in West Germany.  

Also I thought that coil failure normally occurred when the coils heated up, not when they were cold.  This problem is the opposite, when things are warmed up, it starts normally.

Yep it wouldn't start when cold, after multiple multiple attempts, or when warm, it would. When I removed the coils both had cracks in the casing facing the engine. This was an '84 model with the not so good coils.

If the grab handles are a part of the seat, you have the earlier model. There are quite a few other differences between the models.

Hi mate. I could mention a lot of possibilities but then others will probably do this. Look up Bert's won't start guide. Then you can do a proper diagnostic check. It's worth it and once you have that knowledge you will look back. Good luck.

daveyson wrote:Yep it wouldn't start when cold, after multiple multiple attempts, or when warm, it would. When I removed the coils both had cracks in the casing facing the engine. This was an '84 model with the not so good coils.

If the grab handles are a part of the seat, you have the earlier model. There are quite a few other differences between the models.

there are grab handle indentations in the rear of the seat for the passenger so I assume I have an earlier model.  correct?

Post your VIN (last 7 digits) or go to a site which identifies the year and model of your K100RT such as Max BMW or realoem.com/bmw

If you have rubber mounting circles on the main footrest plates then your bike is 1983 thru '85 production. Indents in the seat rather than the rear cowl confirm the same. The exhaust mount of earlier models is also circular. 
 
Curious how you define your bike model as a KRT 100.

Two Wheels Better wrote:Post your VIN (last 7 digits) or go to a site which identifies the year and model of your K100RT such as Max BMW or realoem.com/bmw

If you have rubber mounting circles on the main footrest plates then your bike is 1983 thru '85 production. Indents in the seat rather than the rear cowl confirm the same. The exhaust mount of earlier models is also circular. 
 
Curious how you define your bike model as a KRT 100.

Now you got me curious!  I looked at title and registration and it says "RS".  But it had full farings and both side and rear carriers so it visibly looked RT.  I think the seller I bought from over 10 years ago called it RT.  But it appears to be early model with indents in seat.  On the other hand, the seat is like sitting on a board, and the description of comfort for RS seat matches that.   I have another 85 K100  RT?  as a parts bike so I may switch coils out and see if improvement.

Porto wrote:Hi mate. I could mention a lot of possibilities but then others will probably do this. Look up Bert's won't start guide. Then you can do a proper diagnostic check. It's worth it and once you have that knowledge you will look back. Good luck.

where can I find Berts won't start guide?  Looked around and found a website I was directed to that was expired

Don't trust the rego or title for an accurate description. I worked for years at dealerships. The clerk posting the sale to the DMV for first registration is often the culprit is misnaming models. One K1200RS I owned was labelled Dakar like the early F series singles. I also owned a Triple Black S1000XR which the title clerk labelled Racing Red, and which appeared in the rego and title rather too boldly for my liking. 

"No officer,  it has not had a respray."

And what I meant by being 'curious' is your choice of KRT 100 rather than the typical K100RT, or as BMWAG prefer, K 100 RT. Give us the last seven of your VIN and we can tell you exactly what the model originated from Berlin as, including the production date when it was built. BTW, all 1983 thru '85 seats are interchangeable, as are '86 and beyond with other bricks.

Two Wheels Better wrote:Don't trust the rego or title for an accurate description. I worked for years at dealerships. The clerk posting the sale to the DMV for first registration is often the culprit is misnaming models. One K1200RS I owned was labelled Dakar like the early F series singles. I also owned a Triple Black S1000XR which the title clerk labelled Racing Red, and which appeared in the rego and title rather too boldly for my liking. 

"No officer,  it has not had a respray."

And what I meant by being 'curious' is your choice of KRT 100 rather than the typical K100RT, or as BMWAG prefer, K 100 RT. Give us the last seven of your VIN and we can tell you exactly what the model originated from Berlin as, including the production date when it was built. BTW, all 1983 thru '85 seats are interchangeable, as are '86 and beyond with other bricks.

last digits of VIN is 0XF0051819

That's a 10th month of '84 US market K100RT.
It'd be considered a 1985 model.

Two Wheels Better wrote:That's a 10th month of '84 US market K100RT.
It'd be considered a 1985 model.

Then based on what was previously said I could have coil problems!  I am going to switch out coils from parts bike and see what happens.  Have not ever removed coils from these bikes yet, hope its not a serious issue to do....

In regards to Burts technical info and some other good tech. I'm happy to forward it to anyone via email. portolantechnical@gmail.com
I can't seem to upload it here.
I think some of it came from the motobrick forum.
As for starting up when cold. When running properly they start up , idle and ride away with out problem. No need to turn the fast idle / choke lever past first click. O need to touch the throttle. I'm in below zero temprature a lot and it has no effect on start up. Happy to assist any one, just send me an email.
Cheers

letsgetpractical wrote:

daveyson wrote:Yep it wouldn't start when cold, after multiple multiple attempts, or when warm, it would. When I removed the coils both had cracks in the casing facing the engine. This was an '84 model with the not so good coils.

If the grab handles are a part of the seat, you have the earlier model. There are quite a few other differences between the models.

there are grab handle indentations in the rear of the seat for the passenger so I assume I have an earlier model.  correct?

changed coils, no difference.  Initially starts, conks out and won't start within 30-60 seconds after starting.  then leave alone for a minute or two, and it starts right up. does it repeated for 2 or 3 times, then runs ok with no problems.  Its in the warm up fuel delivery/control but where I do not know.

The replacement coils are probably the old type as well.

Bert's guide describes how to test them, plus a heap of other stuff. It's on this forum, at the portal page click on the tech page, look in the electrical section, it's actually called "Diagnosing the EFI"