Hi My 1990 K100lt is playing up! 
First i noticed a very slight pop or back fire through the air box then it would not take throttle but would not cut out and had intermittent tick over dipping below 1k rpm. left it to cool then it drove 150 miles! so could this be the ignition breaking down?  It did something like this the other week which i taught i fixed but it has not got worse and unpredictable! does this sound like a the ignition trigger plate is failing?  If so is their an after market replacement as the bmw one is lots of £££ . Anyway I was in Ireland and decided to leave it their for now as i will be back in a month or so.  thanks K.

Well now we have lots of HS units hanging around over here would have got you out of trouble. with some 'ELP So where is the K now?

If you drove it 150 miles then it got back up to operating temperature so it might not be the HES.

Other usual suspects for sudden quitting are the ignition switch and fuel tank connector. But, then again, if it's backfiring when it quits then it could be fueling but not getting spark so it could be something to do with the coils.

I agree with Duck about the HES being an unlikely cause.  When the HES are bad, you won't be able to go more than 20 miles before they start acting up.

Fuel issues usually involve sputtering and misfiring while electrical issues are suddenly on and off. 

On the electrical side, the four pin tank connector is notorious for similar problems.  The ignition switch can cause your problems with running along with strange whack with the instrument cluster and the electrical system(lights, etc.).  It is possible but unlikely you have a bad kill switch.  I recall someone having a problem with theirs in the not distant past.  A good cleaning of the contacts corrected that problem.

On the fuel system side, air leaks in the vacuum caps on the throttle bodies, vacuum line to the fuel pressure regulator, and the infamous zig-zag hose from the crankcase to the airbox are responsible for a lot of running problems.

Thanks guys I think i had convinced myself that it must be the hall sensor but had not even considered the kill switch!   As for fuel I had considered the fuel pump but it was running at all times even when the bike was playing up. Just thinking about it if it got below 2.5K rpm that`s when i noticed/appeared to not run right or when i came off the throttle, it appeared to be fine and fully responsive when i accelerated esp aggressively. The bike is now in my brothers house near Gorey Wexford Its is still driving I just left as i had to come back to the UK asap. I will be back over soon to bring it back. 
I did see someone driving a very nice K1 blue and yellow just outside of Geory on Sunday, I wondered if it was one of you guys? K.

I once had a local guy come by with an 85 K100 that ran OK with throttle but idled like crap when warmed up.  Swapped in some different coils and that solved the issue.

dakelvinator wrote:Thanks guys I think i had convinced myself that it must be the hall sensor but had not even considered the kill switch!   As for fuel I had considered the fuel pump but it was running at all times even when the bike was playing up. Just thinking about it if it got below 2.5K rpm that`s when i noticed/appeared to not run right or when i came off the throttle, it appeared to be fine and fully responsive when i accelerated esp aggressively. The bike is now in my brothers house near Gorey Wexford Its is still driving I just left as i had to come back to the UK asap. I will be back over soon to bring it back. 
I did see someone driving a very nice K1 blue and yellow just outside of Geory on Sunday, I wondered if it was one of you guys? K.

If that was Sunday evening may have been one of the guys heading back from the K1 weekend....he lives down that way. 88 was over Gorey way yesterday and has lots of spare bits there too.....

92KK 84WW Olaf wrote:

dakelvinator wrote:Thanks guys I think i had convinced myself that it must be the hall sensor but had not even considered the kill switch!   As for fuel I had considered the fuel pump but it was running at all times even when the bike was playing up. Just thinking about it if it got below 2.5K rpm that`s when i noticed/appeared to not run right or when i came off the throttle, it appeared to be fine and fully responsive when i accelerated esp aggressively. The bike is now in my brothers house near Gorey Wexford Its is still driving I just left as i had to come back to the UK asap. I will be back over soon to bring it back. 
I did see someone driving a very nice K1 blue and yellow just outside of Geory on Sunday, I wondered if it was one of you guys? K.

If that was Sunday evening may have been one of the guys heading back from the K1 weekend....he lives down that way. 88 was over Gorey way yesterday and has lots of spare bits there too.....

I will be back over soon so if my brother has`int fixed it i might be back on hear looking for a bit of help (yet again!). I would have loved to come over for stradbally on the 11th but sadly i am away in Germany, (might be good for parts over there!). thanks again k.

Let us know when you are coming back. We may have a weekend up in Antrim too, plus I am often camping over at Kilkenny and that's less than an hour from Gorey.

92KK 84WW Olaf wrote:Let us know when you are coming back. We may have a weekend up in Antrim too, plus I am often camping over at Kilkenny and that's less than an hour from Gorey.

I will do probably be the end of the month K.

I go along with the comments on the HES too, coil issue may be more likely. Do you recall if the symptoms affected all 4 cylinders or might be 1/4 or else 2/3? A quick test is to swap the coils as they are identical so if the fault follows the coils then you know one is suspect. They are known to break down in heat.

My bike buddy also suggested to me that he TPS can do this too so worth checking it out. I know when I had bad tickover and low rpm running issues on the RT he went at it and it sorted the problem.

On the K100 you can run the bike with the TPS disconnected, that will show if it's that at fault. You can't do this on a K1100 because it needs the Motronic needs the TPS in circuit.

Mike

Sounds like you passed Nicky on his way home to Wexford on the blue K1. As Olaf said, we have bits, let us know if we can help.