Misfire

[Adrian]

I have an 08/1984 model. Here's a couple of somethings I hope someone else has had experience of. Ever since I bought the bike in 1992 it has alway had a slight and occaisional "cough" when trundling along at town speeds - usually about 3000 revs in 3rd. It was always chugging in 4th as the revs dropped too low for the gear.
The only time it dissappeared was when I managed to balance the carbs to wjhat seemed a perfect setting. This lasted a few weeks and then returned back to the slight coughing again. I was never bothered by it as it was so slight and a mechanic friend said it was definitely carbaration and possibly because the internals were getting older. as I'm restoring the bike I'm going to overhaul the carbs anyway but any thoughts on this would be welcome.
The second thing is possibly much more serious. This problem has been with me for about ten years and happens infrequently. The road speed or number of revs is always immaterial when this happens.  The bike will suddenly just "die" as if I had flicked the kill button off. This will last less than a second and then the bike comes back to life with a huge backfire - probably because I don't usually have time to shut the throttle. Recently though - the last year of use - the duration of the loss of electrical power has become long enough to be able to shut the throttle and then pull it back open to restart the motor on the move. A bump start effect if you like.
It has never caused a complet shutdown and it does only happen perhaps once every few months. Any ideas guys???
Sorry its so long and thanks for any help you can give .... Adrian

[Bob_Roller]

Your second problem, I had the same scenario, the bike would completely quit .

I did a lot of night riding and noticed the entire electrical system went dead, all of the lights went out when the engine quit .

Now here's the maddening part, I was told to go through the entire electrical system and check ,clean and resecure all of the connections on the bike .

I did this and it hasn't come back in 15 years now .

I didn't notice  or find anything really out of the ordinary with the electrical connections .

But it's quite obvious that some connection was coming apart on occasion .

No 'smoking gun' to speak of !!!!!!!!!!!!!!!

[benlawlor85]

I think Bobs right. my bike was running very erratically which i put down to a bad coil. But i think it could be corrosion on the contacts... I live in a coastal area and the bike is parked about 20yrds from the sea during the day. I sprayed some batter terminal clean and protect dielectric grease in the contact and everything seems a lot better now.

As for the first problem. When did you last check timing, tappets, carb balancing? my carbs seem to go out of balance very easy...

Ben

[nhmaf]

I think that both of your symptoms may be related, and electrical in nature.   methodical checking and cleaning of connections/wires, relays and switches may be the only way to resolve it.   Sometimes the kill switches (which are getting quite old) can develop intermittent connections, or ignition switch terminals, or coil connections.   Also, are you still running the original gray colored coil?  They can develop tiny cracks and become intermittent.  If you're still running the original coil, I'd just replace it as a matter of course.   Also, has the thermal paste been renewed on the back of the ICU within the past several years?  If it hasn't been, might want to check that too - ICU can heat up and cause engine to die (though all dash panel lights will remain on).   Just chip away at it, but make yourself a list so you know everything you've completed.  Eventually the problem will no longer appear and you can go back to your list to see what it was.

[montmil]

... I was told to go through the entire electrical system and check ,clean and resecure all of the connections on the bike .

I did this and it hasn't come back in 15 years now .

Time consuming, yes, but worthwhile and usually fixes a myriad of little nagging concerns. [smiley=thumbsup.gif]

I will occasionally spend some 'quality time' working just one section of a wiring harness; clean, inspect, dielectric, and re-connect. I'm reminded of the, "If it ain't broke..." homily but, so far, it's all been good.  knock wood

Monte

[tvrla]

Chugging along isn't good for airhead motors. It's called lugging, and what you're doing sounds pretty close to that. Making the engine work below 3,000 RPM is a no no. Just putting through town at 35mph in fourth on a level surface is one thing, but soon as you need to accelerate or climb a slight incline, it's time to shift down and get the RPMs up. These bikes seem to have a reputation for not being durable (we know otherwise) and I suspect it came about from them being lugged. Any boxer engine shouldn't be lugged, but especially these due to the smaller displacement.

As for the second problem, especially pay attention to the grounds. Have you noticed whether anything else goes off when the engine dies? The problem with intermittent electrical faults is one - they're hard to track down, and two - they can be a break in the harness somewhere or a poor connection where the wire is crimped to a terminal. All you can do is hit the likliest suspects first and just keep going from there. The bike is spending its time in one of the worst environments possible for a motor vehicle. It's going to take extra preventative maintenance to keep it in shape.

[Barry]

At a steady 3000 RPM the carbs are in transition from the pilot jet to the needle jet so the two very small transition ports in the venturi just in front of the butterfly are worth checking for an obstruction as perhaps is the pilot jet itself. If you want to confirm which carb circuit is responsible mark the throttle twist grip with bits of tape to indicate 1/4  1/2  3/4 and full throttle then observe the throttle setting when the problem occurs. It may surprise you how little throttle you are using. It's not an exact process as the the twist grip action is not linear but mine would be no more than 1/8 throttle at 3000 rpm which is definitely still in transition from the pilot circuit.

On the sudden dying  I agree it's electrical and it's got to be worth renewing the heat sink paste on the ignition module and then checking all ignition related connections.  

[Sergeant_Joe]

To shut off all things at once would tell me it's an earth problem, BMW likes to group most of it's earth wires in one spot.
So follow all your brown wires under the main frame tube and fined that they all meet at a ring conector, this is your culprit most of the time, clean it up hit it with Vasiline and bolt em up tight.
Also pay attention to the earth strap that bolts into the back of the gearbox at the speedo drive.

[Adrian]

Okay thank you all so much this is all very informative. I will have the bike fully stripped off soon and I intend to replace the electrical bits and bobs under the tank if I think they're too old and cruddy. Apart from the electronic flasher unit and the coil its all as I bought it in 1992. The harness will be off of course so I'll be able to go over all the contacts and wires to check as ou all suggest. Intersting abou the carby transition at 3000 revs. Thanks again guys its all been so helpfull. Adrian ......
 

[Justin B.]

On the R65RS it would occasionally cut out and the tach would go to zero during that time.  I put an ohm-meter between the forks and frame and could see at certain spots in the head rotation I would loose continuity.  I installed a ground strap between forks and frame and it never did it again.  Don't know what might ground through the forks that would cause it to die but maybe it was just a coincidence...

[Dave 2]

So follow all your brown wires under the main frame tube and fined that they all meet at a ring conector, this is your culprit most of the time, clean it up hit it with Vasiline and bolt em up tight.

Here is a picture of the "bundled" Ground wires where they attach with the Voltage regulator. D2

[Dave 2]

OOPS Here is that photo :-?