Random Power Failure

[ddebonis]

Every so often, my bike loses power when I'm riding. It goes quiet, the tach needle drops to zero, and then it usually push-starts it self and comes back to live. If I'm on the highway, it's usually followed by loud back-firing.

This used to be rare, then became common. I did a full tune-up and it seemed to stop. Rode 60 highway miles today and it happened 3 times.

I'm thinking it's likely an electrical issue. And the back firing has to do with excess unburned fuel collecting when the engine dies.

Any thoughts on where to start? Anyone experience something like this?

[georgesgiralt]

My '82 R65 did this a couple of weeks before the bean  can trigger failed...  living the bike dead as a post.
After  replacing the Hall sensor, no more problems so far (8 month riding, everyday)
So you better shop for a new sensor (I tend to prefer the HK101 which is easier to rivet)

[steve hawkins]

Whilst I would agree that it is likely to be an ignition problem, there many places where an intermittent open/short circuit can cause this behavior.  Although the mention of the rev-counter behavior is a useful pointer - it implies that the issue might be low tension ignition as the rev counter is fed from the low tension side of the coil.

Is there any other information you can give us?  What do your lights do when the fault occurs?  Are there any other things happening that you might think are unrelated.  Do you regularly use your kill switch?  

I had a kill switch that was causing me similar issues, for example.  Many people avoid using them, as they are not that robust.

One thing we can be sure - it is electrical. The problem could be vibration related or heat related. And we have some likely candidates.

Intermittent electrical issues can be the worst type of fault to chase.  It might well be the trigger as mentioned above.  

But I think you need to systematic in your investigation.  

I would start by pulling the tank and front engine cover and having a look at the wiring underneath - a visual inspection of your wiring and connectors - just to make sure it is not something obvious. A clamped wire, corrosion or poor connection on your low tension circuit.  Not just in these areas, but underneath you instrument cluster and handlebars.  

I would consider letting the bike run at idle and go round and give a the wiring around your ignition and low tension circuit a light tug to see if you can get the issue to reoccur.  Especially any wires that are not secured and allowed to flap about a bit.  Also around the head stem, as wires in this area are always moving as the handlebars are turning - so give them a few full deflection turns

If you are really lucky you might be able to locate the issue this way.

Once you are happy with all your wiring connections  and wiring - only then would I start changing components.  And then you can look at buying the component Georges mentions above, safe in the knowledge that the rest of the bike looks okay.

Let us know how you get on.

Rev. Light

[jamo]

I had the same problem a few years ago on my 1984 LS. complete failure then the engine starts again with backfiring. The fault was intermittent.
The fault on mine was the ht connection to the coil on the right hand pot the wire had broken from the brass ferule.
The cost of original leads were a joke.
 So a yard of copper ht lead two ngk plug caps two soldered joints.
Hey presto no more problems

[Bob_Roller]

I had the same problem with my '81 R65 .

I was told to go through the electrical system and check all of the connections for security pulled apart all of the connectors checked pins for security and condition .

Never really found the suspect connection but after this work, never came back, going on 17 years now .

This is a frustrating problem to try to isolate as it doesn't last very long .

You're probably riding in daylight conditions so you can't tell, but is the entire electrical system shutting down when this happens ??

I was doing alot of night riding and in my case, I was losing the entire electrical system, as the lighting would quit at the same time .

After learning alot more about the bikes electrical system, one of the few places where the entire electrical system will be affected, is the ignition switch .

Mine failed about 6 months after the electrical problems cleared up, contacts broke off inside the switch, after I removed it, you could shake the switch and hear the parts rattle around inside the switch .

Good luck on your troubleshooting .

[davidpdx]

+1 on your ignition switch. I had the same kind of problem on a Honda 350 years ago before I learned not to have too many keys hanging from the ignition key. When we took the ignition switch apart, the contacts were burnt from being pulled apart by the swinging keys. Worth checking out essentially if you have a heavy key ring or the PO did.  

[ddebonis]

Wow, thanks everyone. I'm relieved to hear I'm not the only one who has experienced this.

From what I can tell, all the lights go out when this happens. It happened once at night so I noticed the headlight go out.

I'll go through all the wiring, and pay careful attention to kill switch (which I do use with each ride) and the ignition.

[Luca]

Another way you can have a total electrical failure is a loose battery connection.  Kind of embarrassed to admit it, but it's happened to me before.  The problem was intermittent, too, although it mostly reared up while I was trying to start the bike.

BTW, your theory on the backfiring is spot on.  I knew a guy who worked at the GM proving grounds back in the day, and he would do this intentionally while going round the track.  Took the engineers only one visit to figure out how his gang was blowing up mufflers