Hello

I have a BMW K75C as my daily bike, and today i experienced that my bike died while standing still and ideling. Afterwards i tried starting it in neautral and with the cluthc in afterwards and it wouldnt start! It crancks over perfectly and it seems that i can hear my fuel pump running. I then had to park it and take a cap to work. After i got home i tried starting it again, and now it started first try without any problems! What could be the issue? and how should i go about finding it. When the bike runs, it runs perfectly and i have no problems what so ever, all of sudden it just cuts out and cant be started for a couple of minuttes/hours.

There'a an almost endless list of fairly straightforward checks:

I'll start you off (let's try and do this is order of easiness): when it next happens, try opening the fuel cap - a blocked vent could cause fuel starvation.

Suzi Q wrote:There'a an almost endless list of fairly straightforward checks:

I'll start you off (let's try and do this is order of easiness): when it next happens, try opening the fuel cap - a blocked vent could cause fuel starvation.

Yes, i tried that, but it didnt help. Didnt thinks it would be a problem since it usually starts

Next easiest to check is the fuel filter. Remove it then blow through it in the direction of fuel flow. If your cheeks look like those in the image below, it is probably clogged and should be replaced.

Laitch re your Post 4. What's the BMW part number for the little critter who clears blocked full filters? How about a group buy!

Good idea, i will check the fuel filter. What about the hall sensor, couldnt that cause problems, or can i rule out the ignition system?

PhillipRambo wrote:Good idea, i will check the fuel filter. What about the hall sensor, couldnt that cause problems, or can i rule out the ignition system?

Bad juju, ancestral curses and corroded ignition switch contacts could also be suspects.   It's best to focus on one thing at at time.

Very generally,
Ignition faults cause an engine to cut out - running fine one minute and then completely dead the next. The exception is a spark plug or HT lead fault which causes misfiring or general poor running.
Fuel faults cause a reluctance to rev, or a weak-feeling engine, or dying out and then re-starting after a few minutes seemingly okay. The exception is an injector fault, which causes misfiring or general poor running, and possibly a reluctance to start.
That's only a rough guide though and, I guess, frustratingly unhelpful.

Suzi Q wrote:That's only a rough guide though and, I guess, frustratingly unhelpful.

Cheer up, Suzi! It could cause an argument.

Suzi Q wrote:Very generally,
Ignition faults cause an engine to cut out - running fine one minute and then completely dead the next. The exception is a spark plug or HT lead fault which causes misfiring or general poor running.
Fuel faults cause a reluctance to rev, or a weak-feeling engine, or dying out and then re-starting after a few minutes seemingly okay. The exception is an injector fault, which causes misfiring or general poor running, and possibly a reluctance to start.
That's only a rough guide though and, I guess, frustratingly unhelpful.

Okay, thanks, i guess i might have to go through it one thing at a time.I will start by going through my wires and making sure there is good ground and generel connection. This is going to take a lot of time

Hall sensor?

Is there a pattern, like the tank is always full when it happens. How long was it idling before it conked out, is the time span a pattern?

92KK 84WW Olaf wrote:Hall sensor?

Yes the hall effect sensor, is a part of the timing of the ignitionsystem if im not mistaken

daveyson wrote:Is there a pattern, like the tank is always full when it happens. How long was it idling before it conked out, is the time span a pattern?

Today i took it for a spin to see if there was a sort of pattern. It started up as usually does, and after i had been driving around the neighborhood for about 7 minuttes it then shut down. Its a immediate shutdown.. . It's just like someone flipped a switch, and the engine goes silent. This has been consistent each time it's happened.

Given this behavior, it think it makes sense to rule out the fuel system as the primary culprit. If there were any issues with the fuel supply or the carburetors, you would likely experience symptoms like sputtering or hesitation before the engine finally gave out. Right? The immediate shutdown without any preceding hiccups suggests that the problem might be related to something other than fuel delivery.

Spark plugs wet or dry?

You got sparks?

The Hall Sensors are a fairly common source of trouble now that most of our bikes are getting over 30 years old. 

A good test would be to get a can of freeze spray and remove the plate that covers the sensors.  Go for a ride and when the engine quits try restarting.  If the engine won't start, then give the sensors a good shot of the freeze spray and try to start again.  If the engine starts after the spray, your sensors are bad and heat sensitive.   This heat sensitivity is a sign of failing sensors and they will need to be replaced.

Point-Seven-five wrote:The Hall Sensors are a fairly common source of trouble now that most of our bikes are getting over 30 years old. 

A good test would be to get a can of freeze spray and remove the plate that covers the sensors.  Go for a ride and when the engine quits try restarting.  If the engine won't start, then give the sensors a good shot of the freeze spray and try to start again.  If the engine starts after the spray, your sensors are bad and heat sensitive.   This heat sensitivity is a sign of failing sensors and they will need to be replaced.

Added to this, do the reverse and when the bike is completely cold take a hair dryer [if you have one] to the T plate and make it hot hot. Then try start.

daveyson wrote:Spark plugs wet or dry?

You got sparks?

Havent checked my sparks conditions, but its a good idea! In the case of no spark what could be the issue then?

Point-Seven-five wrote:The Hall Sensors are a fairly common source of trouble now that most of our bikes are getting over 30 years old. 

A good test would be to get a can of freeze spray and remove the plate that covers the sensors.  Go for a ride and when the engine quits try restarting.  If the engine won't start, then give the sensors a good shot of the freeze spray and try to start again.  If the engine starts after the spray, your sensors are bad and heat sensitive.   This heat sensitivity is a sign of failing sensors and they will need to be replaced.

Thanks! I will try this next time i am in the workshop

"In the case of no spark, what could be the issue then?"

Which plugs don't spark could help to point us in the right direction. 

The pattern seems to be related to heat, so as mentioned, the Hall sensors are a good fit with your symptoms. At start up (engine cold) everything is good. After seven minutes (engine hot) it stops. After a while (engine cooler) it starts again.

If the Hall sensors are good, a bad coil could be another possibility.

Hej Phillip,
A short comment - when trying/getting new Hall Sensor - BUY THE ORIGINAL BOSCH. The cheap ebay/amazon/... once cost you a fraction of the original thing. And that will open up a can of worms like you would not believe.

If the one you have sitting in now is NOT an original Bosch. Start there. AND make sure you get the right one (there is more than one that fit into the machine - but only one version you should use - get the right one).

Drive. Be safe. Have fund (eller: "med hilsner fra djævle-øen")
Jensen

Hej Philip.
My advice is also to use the hairdryer method to test on the Hall sensors. Your symptoms sound like it is intermittend failing Hall sensors. They fail when the engine gets hot. Gets back in working orden when the engine is cooled down.
Endnu en hilsen fra Djævleøen

Regards Jens

Personally, I prefer the freeze spray method because some heat guns can reach temperatures of well over 800F which is more than enough to destroy the Hall Sensors if one is not careful.  Even hair dryers are capable of damaging temperatures. 

There is no way the freeze spray can damage the sensors.

Hello guys, i have tested my hallsensor be heating it up and cooling it down. After i heated it up, it wouldnt start, and when i cooled it down it started again. I have replaced the hallsensor, witch i did by placing it exactly like the previous one was mounted. I was worried that i had to time my engine afterwards, but since i was very careful of how i placed the new one, it didnt have to. Now it starts and runs nice, also went it gets hot!, thanks for the help guys

HALLELUJH, Now buy 2 carry a spare, and ensure it never happens again