R100 cuts out

[OKR100]

I have a 1981 R100T with about 34K miles. I bought it Nov. 05 with 22K miles. It has been a great bike and I was able to go to my first rally in West Bend! Since returning it has developed a troubling problem. While driving, it goes completely dead....and then kicks back in with a loud backfire. This has happened 3 times. Each time the bike had been ridden for at least 10 minutes; it occurred at highway speeds (about 60 mph); and lasted about 5 to 20 seconds before kicking back on. Other than this problem the bike runs great. Starts easy, runs smooth...hey...it's an airhead!

I am a novice mechanic and even less of an electrical person. But I'm trying to learn and willing to dive in. I have removed the gas tank and gone over wiring and connectors without finding anything that looks particularly unusual. Any suggestions as where to start would be appreciated. Thanks!

[20774]

Most likely the problem is electrical...might be fuel related. I'd make sure there's no corrosion at the center terminal of the coil towers where the spark plug wires connect. Could be your spark plug wires are breaking down. What about heat sink past under the ignition control module? Check the jumper wire between the two coils... If both cylinders stop firing, you need to find something that affects both at the same time.

[spof650]

I have to agree with Kurt sounds electrical the sudden back fire and then power is restored
Does it happen again after the first time ?
Does it happen after you hit a bump or any thing like that.
Do you know which cylinder it is ?
You could always try swaping plug wires. or even plugs.


Good luck

[benway]

I would also check/clean the contacts/holder on the starter relay. I think its still under the tank on your year?

the backfire is probably unburned gas in the muffler, igniting.

[lkchris]

Make sure you haven't "sealed" the gas cap by placing tank bag etc. over it to point tank can't "breathe." This will stop fuel flow.

Personally, I'd suspect fuel problems first because the BMW electronic ignition is bulletproof.

[axlray13]

The same thing happened to me. I have an 82 R100 with 19K. I thought I was running out of gas. I would be cruising along and it it would just die. Bad gas or dirt in the tank? I switched to a different gas tank and the same thing happened, when I was merging onto a freeway with a girl on the back. Pretty scary. I'd rotate my petcocks and some how that helped and then it didn't. Finally I discovered that my ignition cannister was bad. Now, smoove sailin...
Axlray

[Boxerkuh]

I think you got a couple of things going on...
1. The bike is asking for some mechanical maintance...
2. You need to find the problem and fix it...

Here is what I would do:
1. Check the spark plugs, if old replace them, are they gapped correctly?
2. Check the carbs, clean them if you have not done it
3. Replace all the fuel lines every 5 years
4. Check the coils, look for bad corrosion and cracks.
5. Check the spark plug wires, replace them if they are over 5 years old
6. If you have no inline fuel filter, I would run the tank dry, take it off, remove the petcocks, replace the petcock filters, and dry the tank out for 3 days...

Remember the bike is 26 years old and you have wear items on them, some need to be replaced by time, others by mileage.... If you take your time and go through the bike, you get to know your bike, replace items before trouble starts and have piece of mind while riding. It is also a great way to get to know Airheads in your area... Join Airheads, call your Airmarshall and you will be on the way... Nothing like somebody showing you the way.... Keep us posted...

[GlobalRider]

While driving, it goes completely dead....and then kicks back in with a loud backfire.

What do you mean by "dead"? Does just the engine quit or does it act as if the key were turned off; by that I mean all the instrument lights go out?

Lets narrow it down with that one first.

[DennisDarrow]

IMHO it is electrical. The odds of it being a gas problem acting on both carbs at the same time are astronomical. Typically, if it is gas, one cylinder will continue to run and you can keep on chugging along on one cylinder. For both cylinders to die simultaneously it has to be something related to the electrical system.

Yes, one needs to know if the whole electrical system is what is effected or is it the ignition. Riding it till it happens again to find this out could leave you stranded on the side of the road as the problem transitions from intermittent to permanent.

Making sure of all connections and possible shorts is the way to go; but I agree, it's probably in the ignition someplace. ...........Dennis

[boxermaf]

I also agree that it is probably electrical in nature - either cracked coil(s) or bad ground (coil bracket crack or coming loose or wire corrosion), or possible a failing "bean can" - this was the first year of electronic ignition, and while they seldom fail, the hall effect sensor in the bean can
does fail from time to time, and this might be the time. I'd pull the tank off and check all the electrical bits around the coil and ignition wiring first, then check to see if anything is shorting out around the diode board under the front engine cover, and then lastly, check the bean can/replace it with another one. Does this happen frequently, only when warm, only when running fast, etc ?

[OKR100]

Thanks for all the input. Some clarification that might help the diagnosis.......when this happens it is sudden and without warning. Seems to be the same as if I were to hit the 'kill' switch on the right handle bar grip. But to tell you the truth, each time it has happened I have not thought to look at the instrument lights, was reacting to traffic, etc and then it started up again. The first time it happened I thought fuel and switched to reserve. But that's not it. When it runs dry, it is not sudden, but sputters a little and I have time to reach down and change to reserve. This problem is instant........running fine.....then dead. Each time it has been at highway speeds and after the bike is warmed up....maybe 10 to 15 minutes after starting out.

[brickrider]

The problem is electrical. There is enough good information from members in this thread to give you plenty of places to begin troubleshooting.

Your last statement is that the problem always occurs after a warmup. This is a classic symptom of coil failure. But don't stop there. If the related electrical components are the same age, then they (plugs, wires, plug caps, whatever, etc.) are at the end of their service life and should be replaced all at the same time - unless you want to troubleshoot some new problem every other time you take a ride. As reliable as these machines are (I put 117,000 on an 83 R100RT), the components do not last forever.

Many components, though they still function, are so degraded that they have a drag effect on the entire system. A typical example is a spark plug. It will give weak spark and run the motor long after it should have been replaced.

Also look for corroded/loose connectors. Get a good service manual. Consider the time getting familiar with the innards as time well spent. And follow through on ALL the suggestions of the members in this thread. The more you discover about the components, whether worn out or still serviceable, the clearer will become the picture of your bike's state of health, and the more troublefree will be your next ride.

[bmdubyou]

Well, I'd be darned if it ain't electrical. I had nearly the SAME thing happen on my 93 GS. Took the tank off & removed every wire connection, sprayed with wd40 & reconnected. That did it...this has been a few months ago and it hasnt happened since. Im not sure which connection was bad because I did them all. I started out with the coil wires & took them to someone to test but he said they were fine. I also replaced the DB (diode board) & VR (voltage regulator) not sure that they all needed replacement but now I should be good to go!

[GlobalRider]

Thanks for all the input. Some clarification that might help the diagnosis.......when this happens it is sudden and without warning. Seems to be the same as if I were to hit the 'kill' switch on the right handle bar grip.

Mine cut out many years ago as if I hit the kill switch. My instrument lights also went out. This is what the problem was:

I don't know if your model year is similar to my '90 model year, but under the right side of the gas tank are 3 or 4 different colored plastic connectors on a fame member. Remove each and inspect the contacts, then taking a fine pointed awl, expand each male bullet connector pin very slightly to enlarge it. That should provide more positive contact with the female pins.

Also remove the rubber boot from your electronic ignition module, then remove the stainless steel retaining clip, then remove the connector and check to see if all pins are fully seated in the connector housing. One of mine, the one going to the kill switch wasn't locked into place. That was another problem when the bike was new causing the slightest hesitation.

[OKR100]

Thank you all for your input. I cleaned as many connectors as I could get 'easily' get to. Bike is equipped with a Luftmeister faring, so I'm not sure if I missed something in the original headlight housing. Spark plugs are good. Cleaned wires, coil brackets & connectors, several wire connectors under fuel tank, removed diode board and cleaned everything under there and all connections. Put it back together and took it for a local spin. Purred like a kitten around town so I took it on the highway for about a 3 mile stretch, did a u-turn and ran back the other way. Did this for about 30 minutes with no hint of a problem.
Sooooo........for now it seems to be good. Today I rode for about 2 hours with no problems. Kind of have the 'waiting for the other shoe to drop' feeling. I plan to look online and see what coils, ignition wires, diode board, etc. cost. Bike is 26 years old and as far as I know, all that is original due to the low mileage when I bought it. Knowing the parts are new will go a long way toward my peace of mind!

Thanks again for the help. It is greatly appreciated!

[RTB781]

I had that happen to a R100R Mystic! I checked everything and talked to the dealer several times. That long and short ofr is that when running in hot weather the battery is charged but loses fluid (acid) to evaporation. My acid level was low and when I added the correct amount of water and brought up the charge-Guess what-no more cut out-which was mostly at high speeds when the most amount of electricity is needed to power things! Simple enough!

[brickrider]

If your bike has a diode board built by Bosch, then it is unlikely to have problems. Years ago, on the early '80s R100 series, BMW changed from Bosch diode boards to a brand called Werle [sp?]. This turned into a disaster, as Werle used cheaper solder (lower temperature rated) and manufacturing shortcuts that became a "when" the diode board went south, rather than "if". This whole issue went 'round and 'round the MOA. So check the diode board closely for any hints that the solder got too hot, melted, and/or ran across other circuit paths, although, again, unlikely if a Bosch. If the diodes check OK with an ohmeter, there's no sense in replacing a good part.

Also, on some of the larger electrical connectors with a lot of pins, one of my favorite tricks was to wrap a small zip tie around it, forcibly holding the connector closed (after cleaning/spraying/lubing the pins, of course).

[20774]

I forget...is the problem with ignition or charging? I thought the bike was cutting out while underway... The Wherle boards were definitely a problem but were on the charging side...

[brickrider]

Today I rode for about 2 hours with no problems. Kind of have the 'waiting for the other shoe to drop' feeling. I plan to look online and see what coils, ignition wires, diode board, etc. cost

I mentioned the diode board issue due to the above quote in OKR100's last reply. There would be no need for diode replacement due to the current problem being discussed. However, just in case he was interested, there is quite a history behind the diode boards, and he might as well be aware of it.

[yukonairhead2]

I have an '81 R100RS, I was lucky enough to drive down from the Yukon this summer to two rallies - one in Menlo Wash. and the second was in Nakusp BC. About 50 Kms from Nakusp my bike died - very similar to your experience - Once i got the bike to the rally there was plenty of help available -we swapped coils, wires, electric modual under the tank no change. Then we swapped out the "bean can" and bingo we struck gold. The bike ran perfectly. Thanks to Chris ( who dropped a valve in his '95 R100 GS) I was able to borrow his ignition canister so I could finish up the 2500 miles home to Whitehorse. I then shipped my old one off to Motorradelektrik for a rebuild - this might be your problem. Enjoy, these bikes might be old but they are great pieces of engineering.

Mike

[GlobalRider]

Then we swapped out the "bean can" and bingo we struck gold. The bike ran perfectly - this might be your problem.

If you think it is, the next time you go for a ride, bring a spare spark plug along.

When it quits, pull off a plug wire (left preferably), insert the spare spare plug and hold it with the spark plug casing against the cylinder head.

Next, with the ignition ON crank it over a few turns with the starter. If you don't see a spark, then with the ignition still ON, flick the kill switch between Run and Off several times. If you see a spark, your pick-up coil in the can (or related wiring) is faulty.

To check that it hasn't remedied itself in those few minutes, turn the engine over with the starter again to confirm that you're still not getting a spark.

Track down Frank Warner's dual pick-up coil mod.

[Na Cl K9]

Thank you all for your input. I cleaned as many connectors as I could get 'easily' get to.,,Cleaned wires, coil brackets & connectors, several wire connectors under fuel tank, removed diode board and cleaned everything under there and all connections. Put it back together and took it for a local spin. Purred like a kitten
I once had a problem like yours with my 83 R100. Every time I got up to speed at around 60 the engine would quit. I started the litany of trouble shooting one system at a time and when I got almost completely through the wiring I finally found the problem. A mouse had eaten (I could clearly see each little bite mark!), nearly through the 4 inch long jumper wire between the coils. With the engine running, pushing the wire a quarter inch towards the rear of the bike caused the engine to die immediately

It then became obvious that as I accelerated up to freeway speeds, the increased wind pressure on the wire under the tank at around 60 mph made it bend back just enough to open the circuit causing the engine to die. After sitting beside the road for a few minutes, the wire would gradually return to it's previous position and the bike would start and run again. Sure enough, a new jumper wire fixed it.