89 k100rs breaking down.

[harper]

New plugs, plug wires, coils and a Hall sensor. Bike still breaks down off idle and backfires. It's my buddys bike. He bought it 600 miles ago. I looked at the work invoices that came with it and found that it had been in the shop several times for the same thing. It has 28K on it and the last owner must have spent a couple grand with this bike in the shop. Invoices for $400-600 were common trying to fix this bike. I replaced all of the above and am about to push the damn thing down a well. The local BMW shop won't touch it as they say we don't work on old bikes. Our shop is busy with the new stuff.  They'll never see another dime out of me with that attitude. I remember a few years ago when they were crying for business. Bad business decision to put off potential buyers and customers.

[frankenduck]

Click here: My K runs like crap at idle but does OK at higher RPMS

More about specific symptoms would be helpful.

[harper]

It just breaks down off idle. When a timing light is used on any cylinder, you can see the miss. This bike has been plagued with the same problem long before my buddy bought it. If I could have seen the sevice records of this bike, I would have told him to pass. I have had the same bike since new and never had any problems like he's had with this one. The engine makes a hard noise like a bang when it backfires and misses. I'm going to tell him to trade the damn thing in at the place that wouldn't work on it !!!!

[frankenduck]

A couple of the usual suspects are the ignition switch and the fuel level sender connector.

I had some local guy who wasted about $500 having a dealer diagnose a failing K75 - fuel pressure, electronics, ICU, HES, etc...  I told him I wasn't a mechanic but that I'd trailer it to my house and take a look at it for him.  Took me about ten minutes to figure out it was a bad ignition switch. He emailed me six months later telling me everything was working great.

Disclaimer: I don't claim to be a guru though. I just have enough experience to know what often fails on these bikes.  I also have basement full of parts which makes swapping diagnosis much easier and inexpensive.

[Rick G]

Of all the BMWs R & K that I have had the only time that I got a true backfire as against a missfire is when the ignition was cutting in and out because of a bad connection somewhere like the switch or a connector or bad earth (not a high resistance but a contact then no contact type of fault). But if a ICU or ECU they would missfire but not backfire.

[Motorandy123]

Well it has to be electrical if you can see it on the timing light. 28K isn't much for the ignition
switch. Did you check the connector on the little ignition box in the front under the tank? It might
get water in it by being in that location.

Put the timing light on each plug wire and see if it is one cylinder or all, then work backward to the fault.

A bad ground or loose fuse could cause a miss. Intermittent kill switch or relay the possibilities are endless.

[harper]

Well, I shot the ignition switch with contact cleaner, still missing (cuts out) and pops. I wired wrapped the plugs and then grounded them, opened the throttle wide, and did a compression test. They all were 145# after eight engine revolutions. I'm just chasing symtoms and not the problem. I just can't lay my finger on the reason this bike runs terrible.
Again, New plugs, new caps and wires , new coils, new Hall sensor, cleaned the ignition switch with contact cleaner, fresh fuel, and lots of frustration. I wholesaled the bike and don't have anything to show for all the work and time.

[ReneZ]

Are the plugs fitted with the little bobbins on the threaded ends and are the spark plugs clean inside?

[Big_B]

I had the same symptoms on my 93 1100rs and found that my positive terminal was actually corroded. The bike would run but misfire and eventually didnt start at all.

[Ramadge]

I had intermittent electrical problems on my 75s for eons.  Tried heaps of things and spent heaps of money.  Read an article that the load sharing relay earths through the starter motor and if that becomes clogged up it causes problems.  Bought some new starter motor brushes and pulled the thing apart.  I have seen dirtier ones in my day, and it didn't look to be a problem, but cleaned it up and put in new brushes.  all problems have now been fixed.  Haven't had an issue since then.  Worth a try.