1990 K75s 106,000 kms
A well maintained bike, has not given me any real problems. So I decided to do a 4 day trip.
It turned out to be 2 days of riding and 2 days of trying to get it home.
The bike was getting hard to keep going after start up on the second day, it would start fine with some sputtering but the battery light would glow dimly while it was running, then the batt light would turn off and it would run perfectly. I assumed the battery needed replacing as it was quite old so found a BMW dealership installed a new battery. But, same problem. I got her going with some difficulty but as soon as I put a load on the engine in first gear it stalled and would not start after that.
I'm thinking alternator, coils, wire set, grounds? I was riding in perfect warm dry weather.
I would appreciate any ideas where to start.
Thanks,
Chris

HI, Had similar problem, I pulled the bike down to clean after purchase and didn't push the ejection lead to the box in hard enough,would run for awhile then start fluttering, some times cutting out completely and other timeswould idle. After starting again it would run fine for a little while then would do this again. It was a real hard to start after washing had to recharge battery was nearly flat again the started,what a relief,didn't think it was ever going to happen,must have sprayed water where its never been.

Hi Chris I would start with the troubleshooting guide in the download section and follow the step by step process report back what you find.
Regards,
K-BIKE

The first steps of your troubleshooting should be to check the connections of the EFI, Electronic ignition, coils and spark plug leads (pull them out of the coils and check the connections), ground connections and spark plugs.
Unplug the throttle position switch as it may be a potential problem too.
An air leak could generate the type of problem described.
Check that the rubber caps on the throttle body are still there and not cracked, the breather hose on the cranckcase and a very important point is the oil filler cap on the cranckcase (The bike will run very badly if its not tight).
These checks don't require any special tools or money to be spent.
After this, you should check the fuel supply (fuel filter) and pressure regulator.

Bert

Thanks guys, I've checked just about every connection, all fine. No air leaks that I can see, rubber in good shape.
Put it all back together and tried to start it, out of 4 tries only once did the engine spin freely, the other 3 tries the starter stopped or was stopped after a second or two. Do you think it's possible the starter clutch to be jamming and stopping the engine from turning resulting in a stall?

Hi there
I´ll check the fuel filter... your description remind me of something.
Best regards
JAP

Chris,

I don't think the starter clutch couldn't jam your engine. If its bad, the engine will not turn with the starter or the starter would turn all the time when the engine is running.
What puzzle me is that the problem started with the charging light glowing when riding.... Your alternator may have a mechanical problem.
The easiest way to find out is to remove it.
The alternator is attached by only 3 screws and it takes only 10 minutes to remove it.
You can run the bike without the alternator as long as the battery is charged. At this point, you have only 1/2 hour labour to lose to explore this possibility.

Bert

Bert and all, I pulled the alternator and starter. The alternator's rubber dampers are a bit worn but the unit spins freely with nothing loose, the starter on the other hand seems stiff. When power is applied to the starter
the speed ramps up to full speed in 2-3 seconds then stops very quickly once
the power is removed. This is the first BMW motorcycle starter I have dealt
with but every other starter, BMW or otherwise worked just the opposite.
Quick to spin up and slow to spin down with no load. I haven't opened it yet,
I put the bike in 5th gear and spun the rear wheel to make sure the engine actually turned without obstructions.

Chris,

I would say that it would be a good time to open the starter and check the brushes.
One of the known problem of the K's starter is the magnets on the stator becoming lose. At some point, the lose magnet may be jamming the starter.
I don't believe that your original problem is related to the starter, but a bad starter will create all kind of crazy problems.....
Here is a couple of tutorials on how to open the starter

My single strand battery ground wire had an intermittent Open underneath the insulation which caused all kinds of problems. When I jumped the bike I bypassed the problem by grounding on the frame. I had symptoms of low battery, bad battery, bad alternator - could jump but I needed throttle to keep running. Don't just check the terminals. I went through what I thought were batteries on this problem.

Been away in Aus for work so the sudden stop does indeed sound like the pole pieces have come loose and are physically jamming the starter.
Regards,
K-BIKE

Well I'm stumped. Took apart the starter, everything looked fine inside, re-assembled and tested works fine still a bit stiff but maybe that's the way they are. With the Alt. in or out she won't start, it will turn over twice then stop. Turn the key off then on again hit the starter button, two turn overs then stop dead. The only difference now is I no longer have a battery light coming on on the instrument cluster. Could this be the starter relay, is there any way of testing it?
Thanks,
Chris

Hi Chris,
Did you measure the voltage on the battery when the starter is running and did you do the same at the starter itself because that will tell you if the voltage to run the starter is disappearing for some reason and hence why the starter is stopping so to speak. If power is still at the starter when it stops consider trying will the bike turn over with the plugs out and the engine in high or top gear (to reduce the effort of pushing). Just trying to eliminate the question of the engine physically jamming.
Regards,
K-BIKE

Engine is turning over K-bike. I'm thinking after some more testing this afternoon that it must be the starter relay. The starter motor will not turn over anymore from pushing the starter button. It will only turn over if I jumper power to it straight from the battery. Also, there is no voltage reading on the #87 terminal of the starter relay while the starter button is being pushed, while there is a full voltage reading on the #30 terminal.
I have also purchased from ebay a starter motor that looks pretty fresh
but it won't be here for a couple of weeks. As Bert says "A bad starter can cause all sorts of problems.
I don't mean to sound like I know what I'm doing here because I don't.
Electricals and especially electronics baffle me generally.
If anyone has any ideas....
Haybartender, I am going to check through every wire this winter but I really would like to get it going and figure out what this problem is before I disassemble the bike for its resto.

Hi Chris,
Can I suggest that you do the following check use a test light or a meter to confirm you have voltage on the cable from the start button even when the motor stopped and the start button is pressed. I suspect that when you push the start button that you are losing the power and the relay coil is turning off. You could have a faulty clutch switch or another break in the supply to the starter push button if you lose supply from the starter switch the problem is not the relay nor the starter motor it is the loss of coil voltage to the starter relay.
Regards,
K-BIKE

K-Bike, you might be on to something there, I have done a connection to connection continuity test on all the wires coming from the battery to the starter switch and back down to the starter relay BUT now that you mention a possible faulty clutch switch I remember one of the few times I got the engine going during my testing that I squeezed the clutch lever in and the engine died. I had forgot that had happened, had not considered the clutch switch a possible culprit. I guess that clutch switch is buried inside the the clutch lever assembly??
I was doing some reading in the archives of another K bike forum, the Yahoo group and seems that the Load Shedding Relay is also one of the usual suspects with this sort of failure so I'll be checking that this weekend when I get some unbroken time. While hunting around I found a place in Texas that sells the same starter relay for half to a third of what BMW wants. I'll post the address in my next post.
Thanks K-bike! Gives me somewhere to search while waiting for new parts to come in.

Update, got my new used starter in the mail yesterday and installed it,
pushed the starter button - nothing. Pulled the clutch lever in and the engine spun over. So I went straight to the clutch lever switch and found that one of the wires right at the switch had broken off with fatigue but was still touching sometimes. I love it !!! I actually found something I can fix! Thanks again K-BIKE.
So, I have ordered that switch/cable combo, in the mean time I jumperd the connection to eliminate that problem. (seems like I have at least 2 things going on here and maybe more, but we'll see)
With the clutch lever switch problem temporarily solved I pushed the starter button and I now have consistent turnover of the engine, but it's not starting. I am noticing occassional puffs of exhaust but it doesn't sound like it is close to starting. I connected the multimeter and got 15.15 volts at the battery, I also did a load test and it was good - better be, it's brand new. With the key on I got 14.80V , pushed the starter button and the as the starter and engine spin it reads 12.8 - 13.5, let go the starter button and the battery bounces back to 14.8 in seconds. While pushing the starter button and testing at the starter I get 9.0 - 12.85V but it is fluctuating.
So, for an engine to start it needs air, fuel and spark, the air filter is new, I removed the plugs and they were soaked with gas, the fuel filter is new but I took it out and flushed it and blew it out just in case.
Spark, Is there anyway to test it without getting zapped?
Thanks,
Chris

87m6chris wrote: Spark, Is there anyway to test it without getting zapped?
Thanks,
Chris

Yep, ask your wife to hold your hand when testing the spark plug. You won't feel anything, but she will get the jolt.....

Seriously, just use a pair of insulated pliers to hold the spark plug cap.
If your bike is really flooded, it may take some perseverance to restart it. When this happens, I use a small blow torch to burn the excess of gas in the cylinders. I remove the spark plugs and direct the flame toward the spark plug hole (1/2 second per cylinder is enough). Don't stay in line with the cylinder as it may produce a small explosion in the chamber. When it's time to re-install the spark plugs, I pre-heat them with the blow torch.

Now, as your wife already got zapped when testing the plugs, be kind and don't ask her to hold the torch

Update,
So, it wasn't the spark!
It was a combination of the clutch switch, which is now working with new parts, and a vacuum hose. The one with the loose spring winding/cage on the last throttle body.
Heat had formed the rubber tube into the shape that held it in place but the rubber of the hose had shrunken around the brass intake tube and was letting in air and screwing up the formula.
And all I had to do was take a blade and cut off 1/2" of tubing and all is well.
AAGGHHH! I knew it would be something simple like that.

THANK YOU to all that help me.
The season is pretty much over for me as I want to do some timing chain work and upgrades on the brakes and add some hand warmers and new HD wiring for the head light and horns.
Thanks,
Chris

Hi Chris,
Just a thought from some friends who ride a lot in the cold consider a heated vest and gloves they are more effective than the heated grips.
Regards,
K-BIKE