I have a weird fault with ny BMW K100 RS. When I filled the tank with petrol, the bike wont start. If I roll it down hill it will bump start, and if I leave it 40 mins it will start then. All other times its starts first time, even when realy cold or realy hot. I have changed the fuel filter but it made no difference. Could it be the fuel regulator? Any Ideas? Has anyone had similar problems?

Quick way to tell if it is the pressure regulator that is causing a problem is to measure the pressure to ensure it is around 36 psi.
Regards,
K-BIKE

Hi there, the bike wont start because the starter is not working? or the starter works (and spins the engine) but engine wont go on?.
I´m thinking about dirty starter syndrome.
Best regards
JAP

Ok but, the bike starts frist time every time except when i Fill the tank with petrol, how does that relate to dirty starter syndrome. What is dirtystarter syndrome?

This doesn't make any sense to me. Have you tried to start the bike with the gas cap open?

Same opinion bert, blocked fuel air hole in cap. Once had a yamaha that was startfirst time, always. After a good wax no start , had blocked air hole with wax. 3 HOURS TO FIND!!!!!
Also your not filling it to brim? mistake i made with mine when i first had her, opened cap to let air in and fine ,now i just make sure to fill to plastic rim of filler.
pete

Mickc
The K starter Gremlins are not very reasonable, I dicovered mine because the bike failed to start at the gas station, not wen the bike had sometime parked, reasons? cant tell for sure but maybe its not the same to stop for gas and restart, than stop to eat, in terms of starter´s dirt electrical behavior. The fact that wen the fail occurs the bike jump starts, reminds me the trick to start by engaging a gear and moving the bike a little so the starter will work propperly.
Back to your question the dirty starter sindrome is a series of diverse and some times random, electrical failures (ligths wont glow or turn dim, starter wont work, ignition may fail, instruments going crazy) that happens wen the starter brushes are dirty or worn, and the ground thru the starter is not good. The cure is simple, take out te starter, check and clean or replace. If the failure persists, or you find another explanation, please let us know.
Best regards
JAP

I'm not voting for blocked tank vent. Why would it pop start then? The fact it pop starts means there is fuel supply. Mick, what is your procedure for filling up with fuel? I'm thinking electrical issue that gets disturbed when fueling. Do you shut down with the kill switch, or just turn off the ignition? Maybe the side stand switch?

When I stopp the engine I always just switch off with the ignition key. When I filled up with fuel and it does not start I have tried opening the tank cap to releive any pressure but that did not make any difference either. At the moment I have to make sure I use a petrol station on a hill so I can bump start it. I have tired starting with the throttle closed ( This is how I always start it at other times) and I have tried it with the throttle open, but no difference. I have not chaged the air filter for years could that be a possible cause.? As for the side stand switch, I disabled that with its linkage to the clutch lever years ago, so that can't be the cause.

Just Replying to japuentes:- The starter motor spins the engine over ok and there seems plenty of life in the battery. So I can't see it being electrical, unless it has something to do with the "HALL SENSORS" which tell the eci what temperature the ambient air is. I think an ari filter replacement should be done. I got one with the bike, The previous owner had ben putting it off because it is supposed to be a pig to fit. ( and Thats why I have not done it) I will have to bite the bullet and do it I think.

Just a thought, the tank gets heavier when full compared to empty, is it pressing down on something such as the cable that feeds the fuel pump or the plug and socket that feeds that cable?
Regards,
K-BIKE

Was also thinking about that same thing exactly.

Hi K-bike and Club-C. Latest development is: I filled up the bike today and sure enough it would not start. So rolled it down hill and bump started it ok. When I got home. I switched off the ignition and opened the tank cap, then closed it and tried starting. It would not start . therfore It looks like It must be a pressure thing. Either the breather is blocked ( I have tried running a wire down it, but will next try blowing it through with the foot pump.) Does anyone know where the tank breather hole goes to? The tank breather is that small hole in the filler rim I assume. How does the air get past the tank cap? Is there a hole in the tank cap? So looks like four possibilities :- 1Tank breather blocked . Tank filler cap breather blocked, 3 tank presure relase valve faulty or 4 pressure regulator Duff. Will let you know. But much appreciate any thoughts you may have on the matter .

Try lifting the tank slightly by removing the 2 screws at the back of the tank under the seat. You know the ones? And then try starting it. This would alleviate the heavy tank squishing wiring theory.

I don't think it's the tank vent. If the tank was open, as with filling up, the engine would die after eventually being starved, so not immediately. The tank vent as well as the drain from the tank lid recess end as the two little pipe stubbs at the right rear bottom of the tank.
The not starting can only be an electrical thing for me.

Things are looking up, Fingers crossed. Yesterday I dismantled the fuel filler cap. Iside there was some grease and some grey sludge in the underside of the keyhole lock. I brushed it with petrol and cleaned it out with a needle and cloth. I also blew air through the vent hole in the filler rim. After riding home today I switched off the engine and opened the tank lid. 1 then closed it and tried starting the engine and it worked ok. I won't call it fixed yet until I have tried it a few more times. Will keep you posted.

Be sure to leave some grease in the lock cylinder of the petrol cap. It is there to lube as well as to keep moisture out.

good thinking mike .......

The other ting that gets turned around is the drain vent in the petrol cap assembly. When the cap is open there is a small drain hole which is intended to drain water from the area around the cap when it is wet and allow it to run away down a drain tube. Sometimes when changing the fuel filter people get the rubber washer and the cap 180 degrees out so the recess does not drain. A simple check and easy to fix by taking out the screws and rotating the rubber washer.
Regards,
K-BIKE

I have filled the tank recently and the bike did start ok. It took a bit more turning over than usual bit it started. I have done two things at the same time so it is difficult to say which was causing the problem. I dismantled the filler cap and cleaned it and I also blew out the drain/vent hole in the rim of the tank filler. Question is If one of these was blocked which it must have been; did it cause pressure to build up or did it cause a partial vaccum ? Would either of these conditions adversely affect the fuel pressure sensor? and prevent bthe bike starting? Any way it seems to be ok now. Only trouble is my clutch appears to be slipping. Has anyone out there changed the friction plate in the clutch? it has done 57k I was wondering if it was a big/dificult job?

Mickc,

57K is not a lot for a clutch. You should first check the setting of the clutch. Click here for a good tutorial
There is a hole on the bottom of the clutch bell housing. Do you see any mark of oil in this area? It could be your output shaft seal leaking.
If the clutch has to be replaced, I would certainly replace the output shaft seal too. This is not a big job and it could be done in a day.

Thanks (crazy Frog) for that info . i have printed it off. I can get a friction plate for £63 and looking at the article it looks like I could do it. I will certainly check the adjustment first and the Oil thing, before embarking on changing the friction plate. Mind you If I have to do the O ring I might as well do friction plate as well. Cheers.

I was not talking about the O ring. The O ring has to be changed every time you remove it. I was talking about the output shaft seal (#6).



Also, check this post. It can make your life a lot easier.

Sorry about that Misunderstanding Cray frog. I checked for any oil around the hole under the crakcase. it was dry No oil Phew! Relief. Have since checked the opearting lever, cable and Arm on the crankcase. It was totaly siezed up due to all the bad weather during the winter. I cleaned it all up and worked the arm free using Plus Gas spray and eventualy got it quite loose. I did not have time to remove the pivot spindle through the arm, so I will have to do a proper job later. Anyway it is now working ok. No slipping clutch, but I will have to replace the cable asap, as a couple of wire strands are broken. Many thanks for all of your help everyone!

Great job! all is (almost) good with minimum expenses (I guess the only one would be the cable).
This is the way we like it!