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I am tracking down a loss of power, rough idle and hard starting problem my 83 r100cs. The bike has always been a cold starting beast which requires the choke on for several long minutes. After talking about it at a resent tech day.. I thought maybe its time to replace these older things to set it straight. So now I am working my way from new plugs to new wires to the coils to maybe the ignition. The original 30 year old BMW factory cables which were replaced last had the coil metal contacts that laid on the outside of the insulating wire. It formed a nearly complete encapsulating contact end. The ones I put in are more of a sleeve type which were inexpensive. Being ignorant of this.. Which ends are better. Ted Porter and BMW seem to like the barrel ends...

To continue this story.. The bike did start up and I rode it for a few blocks. The bike stopped after a warm up. Once cooled down it started up again and was able to ridden home.

It would be nice to have this squared away so I don't need cancel the ride to the annual Airhead Death Valley Rendezvous.

Ridercam wrote: To continue this story.. The bike did start up and I rode it for a few blocks. The bike stopped after a warm up. Once cooled down it started up again and was able to ridden home.

I'd suggesting changing the coils (or is it a twin fire coil) sooner rather than later. The above symptoms are classic for a faulty coil. There was a lot of discussion here recently in the following thread:

http://boxerworks.com/forum/viewtopic.php?f=1&t=1524

In short, as coils heat up in normal use the internal wiring can squirm around with the heat. If there's a break in the winding it can open up with the heat, only to close again when the coil cools. Also there is a insulating varnish on the windings which can deteriorate and short the a winding on the coil to it's neighbors, only to resume it's separation from its neighbor as the coil cools.

On a bike with even suspect coils I would be inclined to spring for new ones. I would regard it as good preventative maintenance even if the problem turns out to be something else.



Ken, been there, done that in Oklahoma

Yes, I agree with Ken. Good preventative maintainance.
I have recently replaced the original grey coil (Still working)
and ignition control module with new EME units.
There was no noticeable difference in performance.
I noted that a PO had the +ve and -ve wires on the
wrong terminals as these are plainly marked.
I fitted the new coil and corrected the wiring; again there
was no difference in performance.
If the wiring works either way, why bother to mark the
positive and negative poles ??

i agree with Ken,on the coil thing, but I might suggest if you haven't already check your valve adjustment, out of adjustment valves can cause hard starting, poor idle and hurt the power and it doesn't cost anything to check them.

Richard T in snowy central Okla

According to Dave Vizard in his book -How to build horsepower- the theory with the coil polarity is that it requires less voltage if the spark jumps in the correct direction, so you will get a stronger spark if you have the coil correctly connected.

However, I read somewhere that BMWs twin coil has one spark going each direction anyway, and if this is correct then it wont make a difference, except perhaps to the models with a electronic revcounter.

I spoke to Ted Porter of the beemershop. He gave me some interesting insight concerning the coils. He said he does not carry coils from those 30 years of experience as he has very rarely found them faulty save for physical damage due to impact, fatigue or see how some owners who enthusiastically jammed bad spark plug wires into the coils... Furthermore, he firmly disagreed using ones that don't have barrel ends - he said it never pays to skimp on those. He suggested to first replace ignition wires again with the better ones... His or oem BMW barrels ends. Secondly his suggestion was to look at the ignition control unit and replace that too using heat paste. Then clean the carbs vents and jets again with carb cleaner blowing out the main jet too. Then see how it goes after start up. if it is faulting after that... Then I need to do some ignition sending testing and testing the spark for strength and color.

The good news is that I will have robust electrical system once settled.

man do I love this bike... Any other thing that I own starting this level of acting up including my 10 year old would be on craigs list.

Ridercam wrote:I spoke to Ted Porter of the beemershop. He gave me some interesting insight concerning the coils. He said he does not carry coils from those 30 years of experience as he has never found them faulty save for physical damage due to impact or see how some owners who enthusiastically jammed bad spark plug wires into the coils... Furthermore, he firmly disagreed using ones that don't have barrel ends - he said it never pays to skimp on those. He suggested to first replace ignition wires again with the better ones... His or oem BMW barrels ends. Secondly his suggestion was to look at the ignition control unit and replace that too using heat paste. Then clean the carbs vents and jets again with carb cleaner blowing out the main jet too. Then see how it goes after start up. if it is faulting after that... Then I need to do some ignition sending testing and testing the spark for strength and color.

The good news is that I will have robust electrical system once settled.

man do I love this bike... Any other thing that I own starting this level of acting up including my 10 year old would be on craigs list.

All due respect to Ted, if you have correctly understood him, them much of what he has told you flies in the face of every single experienced mechanic I know, both professional and amateur. And some of what he has told you is unquestionably dead wrong.

There is no way that ANYTHING having to do with the carbs can have ANTHING to do with the bike quitting when hot and not firing again until cooled off. The possibility of it being a a different electronic component failing when hot is not impossible, but the carbs are simply not involved.

Replacing the plug wires on a thirty year-old bike is perfectly reasonable advice, but the symptoms are not related to plug wires, and brand new plug wires can sometimes help weak failing coils limp along a bit longer, although it is a band-aid that is not curing the real problem.

To my mind, it is simply impossible that he has never, in all his years, run into failed coils on these bikes, when everyone else in the industry finds this to be a very common failure after 25 years or so (and not just on BMW's). Not to mention that your symptom of dead when hot and reviving when cooled off is the classic well known symptom of of failing/failed coils. It is extremely difficult to understand how he could have made such a statement.

Come on Major, you really want to say something, spit it out.

Major... This is the correction I made to my post. Poor choice of words written from my iphone. I hope this satifies your correct distinction. [quote="Ridercam"I spoke to Ted Porter of the beemershop. ... as he has very rarely found them faulty save for physical damage due to impact, fatigue or see how some owners who enthusiastically jammed bad spark plug wires into the coils...]

As for his advice, I trust his opinion as he remotely tried to help me. I know there are many here who are brilliant with these machines. I also know that I am both am semi-ingnorant and quite the amateur in diagnosis, repair and now technical writing.

On other vehicles I have seen a bad electronic control module will fail when hot, and work again cold, but only a couple of times before total failure.