Today I finally found some time to fit the replacement FPR I ordered recently. After much faffing around and removing the air box/filter assembly etc. I finally laid eyes on my nemesis (the FPR)! Having skinned a few knuckles and cleaning up the area under the (now removed) airbox assembly, ok I got sidetracked. I could see the beast in all its grimy glory. Removal was not quite as straightforward as I had been hoping, obviously when originally fitted the entire fuel rail was pre-assembled and installed as a whole unit, I managed to get the blighter off and once in my hands I tried blowing/sucking on the various inlets and outlets. Sucking on the vacuum pipe nozzle got me nothing and neither did blowing through it. Next I tried blowing/sucking through both fuel feed nozzle and return nozzle, there was no restriction at all on either and I could easily blow through both - not sure what that means diagnostically but when I tried the same with the new/secondhand replacement FPR I was unable to blow or suck through either. Whilst I was in the area of the rear of the fuel rail I noticed another unit attached to the rail towards the front of the motorcycle which clearly had electrical connections going to it. In true spirit of adventure I investigated this mysterious device (please enlighten me as to what purpose it serves), it looks like a sensor of some sort. I jiggled its wires and one of them promptly fell off in my hand - clearly this wasn't right. Anyways, I figured that all electrical connections should be tightly fitted whatever their purpose so I used the magical cleaning spray so often mentioned on this forum, cleaned and tightened both electrical connections and rehoused them in their rubber sleeve (could this have been my problem all along I pondered ?) and got back to the FPR. At this point I suddenly realised the time and had to rush off and see a lady customer with a poorly computer. I was reeking of oil and fuel but luckily she was very understanding. So, my next task is to reassemble and reconnect all that I have made asunder and see where I stand. All things being equal and if there is a god of old BMW motorcycles and their owners out there somewhere, something I have done/changed/made good will make the old girl run like clockwork again. I have certainly become much more intimate with my K during this period and am mostly enjoying the learning process.

P.S. If anybody can tell me what that unit forward of the FPR on the fuel rail (2 wire connection) is for I would be most grateful.

That is the temperature sensor and is quite possibly the source of all the problems. There are 2 sensors in 1 housing one for the ECU the other for the fan so make sure the wires go back in the right place as you can't just turn the plug up the other way.
When a wire is off the resistance is infinate so the ECU goes full rich because it thinks it is very cold.

K Freak wrote:That is the temperature sensor and is quite possibly the source of all the problems. There are 2 sensors in 1 housing one for the ECU the other for the fan so make sure the wires go back in the right place as you can't just turn the plug up the other way.
When a wire is off the resistance is infinate so the ECU goes full rich because it thinks it is very cold.

Thank you for your most valued input K Freak - I guessed that the component would not have been included if it was not important in some German way of thinking ! The wires have definitely now been made good and gone back on the correct connections - could it possibly be that this was the problem all along ? I will not know for sure until I reassemble the rest of the bits I guess. However, I felt that the fact that one of the wires was hanging off could not be a good thing and whatever else may come of this whole frustrating exercise it may well be that I have no need to go back to this area of the engine for some time to come. I will as always update you when it is all back together once again. Thanks again to all the members of this forum for not losing patience with me yet

Yes , i ordered a new sensor (water and fan) and was sent one for a k1100, spent a few days scratching my head and frowning as to why this b@stard wont run now, but on the upside, that area under the airbox and behind the throttle bodies is clean as, and i know how my bike goes together .
hope you have it sorted krambo.

N.

partially connecting cables is ..ALWAYS...a problem ....(dang if i could get all that searching time back )

good work finding your ails ....happy riding !!!

Krambo,

Your model has a ball and spring restricter on the fuel return to the tank. I removed both spring and ball and that solved my problem. Later tanks had a high tube doing away with this valve.

By removing the valve innards you need to plug it with a blanked pipe when removing the tank. Hope this helps.

I always go for the simple things and find mostly they are the reasons for failure. It can cost a fortune by keep replacing parts.

My two penniworth.

Thank you for your comment Ajays (and Happy Birthday), if you had followed the whole topic through you would have noted that I actually have a later/replacement tank on my K100 (the one where the return feeds back to the tank towards the top left front and not the early type with ball/spring arrangement).

Thanks again for your input - I hope to report back with a positive outcome within the next week or so

krambo,

You have to make allowances for us old uns....I will follow this as I would love to see you solve it. And I'll read it all.

Ajays

um krambo ...i also have a later model one with the return at the front left ....but a spring and ball it does have ....you should hear that little sucker rattle ........its a good sign for me ....ill get round to extending the port to the top of the tank like bert suggests ....one of these days when i can get off the thing long enough ....summer is here ..!!

charlie99 wrote:um krambo ...i also have a later model one with the return at the front left ....but a spring and ball it does have ....you should hear that little sucker rattle ........its a good sign for me ....ill get round to extending the port to the top of the tank like bert suggests ....one of these days when i can get off the thing long enough ....summer is here ..!!

That is interesting charlie99 - I had assumed because I could see fuel returning to the top left front of the tank that my later tank didn't have the ball and spring arrangement. However, having read other posts on this forum it would appear that one symptom of this ball/spring blocking is the fuel pump working overtime - this was definitely the case with my problem ! ? I am always open to suggestions and if my other "repairs" do not cure the problem then that is surely the area I will be looking at next - I will be gutted if that is what it turns out to be, having spent many hours wrangling with this issue

hey mate still got my fingers crossed for ya ....



as ajays says there are in fact several models of the return setup ....lets hope yours is in fact one of the later ones ....i believe there is a transition time between maybe 85 and 87 when (depending on local imports ) you got the older style or the newer one with the high lift setup



just wanna see you get that beast out on the road reliably mate ...

Well - I spent a couple of hours working on the bike this afternoon following my replacement of the FPR etc. (Why did they make the airbox cover such a pig to clip back together?) I re-cleaned the black/sooty plugs and tentatively pressed the starter button hoping for a positive result after all my labours but it was not to be! Once the fuel rail had re-pressurised the bike started up ok although the battery by this time had got quite low, I then removed the fuel filler cap once again in order to observe inner tank activity etc. and it seems that charlie99 may well have been correct all along Had a little more daylight on my side today and I noticed that the fuel return inside the tank does not in fact feed to top left of tank as I had thought but enters the tank into a seemingly blanked off stubby upside down cylinder type thing (approx 1½" height, 1" diameter) inside the tank. This sounds to me very much like the troublesome ball/spring assembly previously mentioned in this topic ! I also noted that there seemed to be quite a few air bubbles gathering around the bottom of the tank around the junction where the 4 pin electrical connector enters the tank (long black plastic tube with wires exiting to pump at top). I think this might be what I had mistakenly taken for fuel returning to tank when the tank had more fuel in it. I feel like an idiot now because it seems that my replacement tank is probably the same as the one it replaced (that's eBay for you). It is difficult to say at this point whether any of my efforts have made a difference because: a) battery is almost flat and b) there is very little fuel remaining in the tank. Once again I was defeated by darkness and I will attack the issues with new vigour at the weekend if time permits. At least I know that the originally suspect parts have been replaced/made good during this time and I have learned a lot more about how my "K" all fits together. Now I must go and look for a topic about the damn ball/spring fuel return and how to deal with it - incidentally, and for the resident experts here, when I went to refit the tank (which had been stored on its side), fuel pissed out off the return pipe and all down my arm whilst I was trying to re-attach the fuel pipes etc. which is what made me take a closer look at the tank internals - so clearly the non-return valve (ball/spring) isn't working anyway so maybe some PO has already removed the offending bits. I look forward to any comments/suggestions from our knowledgeable members

P.S. I really look forward to the time when I can post that all issues have been resolved and that bike is now up and running properly again

krambo wrote:P.S. I really look forward to the time when I can post that all issues have been resolved and that bike is now up and running properly again

lols it will never happen ....giggle ,,,,the old rubbers will keep us diving in there every now and again till they are all replaced ...bearing seals and all ....but ....there will be a sweet time of good riding .....enjoy when you can mate

Krambo,

Never attempt to try starting with a low battery or you will weld the relay points together. Another twopenniworth.

Ajays

Some news for all forum members that have followed my exploits/frustrations/heartaches etc. whilst trying to get my old 1984 K100 back into a running condition. Following on from my last post I managed to catch a spare hour of daylight today and revisited the garage. The battery had charged up nicely overnight so I decided to review all of the steps/work I have undertaken so far whilst trying to get to the bottom of the poor running/bogging under throttle etc. I then decided to retrace the steps I took to replace the FPR and make good the temperature sensor connections etc. I double checked all of my work - all seemed good on the right hand (airbox) side of the bike but rough running still happening! Then (in a eureka moment) I remembered that I had disconnected the crankcase breather to plenum pipe (I had been unsure whether or not this was necessary to take the airbox apart etc.). I hastily reconnected said hose, tightened it up and with some trepidation pressed the starter button, hardly daring to hope that all might now be well. The old girl started on the button and settled into a nice even tickover with cold start lever about halfway. I let her warm for a while before trying to apply any throttle (I was very nervous at this point - lol) after just a few minutes and with twilight closing in I tentatively approached the throttle, held my breath and gave her a handful. Hallelujah - no missing/stuttering at all, everything looking and sounding normal in the fuel tank. I left her idling again for a minute or two more as the problem never had showed up immediately anyway! All continued normally inside and outside the fuel tank (lovely stream of returning fuel in front left of tank) engine sounding sweet etc. Could I dare to hope that I had finally cured the problem ? After more than an hour of stopping/restarting and even a quick ride up the road and back illegally (no MOT or Road Tax) it seems that I have finally prevailed and the old girl is running just as sweetly as when me 'n her did 4,500 odd miles around Europe two years ago. (She has been off the road since September 2010)

Huge thanks to all those on this forum that have helped me to achieve a positive result with their valued/knowledgeable input - you all know who you are!

I think a couple of cold ones might be enjoyed in my house tonight

Congrat Krambo.

This is what an air leak will do.
Now, warm up your engine, and slowly open the oil filler plug. you will replicate the problem at the exception that the air comes comes from another area.

Enjoy your cold one.

CF

yipeee !!!

excellent job Krambo hope you replaced that hose with a new one so you don't have more trouble down the track

Toto_jp wrote:excellent job Krambo hope you replaced that hose with a new one so you don't have more trouble down the track

The hose was new anyway Toto_jp - yet another of the bits I had replaced on my journey to eventual success - I had simply forgotten to reconnect it in my eagerness to check if all my other repairs had been successful

Glad you have it sorted Krambo. After all that you certainly deserve a long ride.

K Freak wrote:Glad you have it sorted Krambo. After all that you certainly deserve a long ride.

Thanks for that K Freak, it really is a huge relief and I am pleased that I managed to sort it out without resorting to expensive BMW service agents - thanks once more to the knowledge and dedication of this forum's members. I might even tax and test (legalise) the old girl and take her for that long ride that you suggest.

P.S. The beer tastes better than ever this evening

Well done Krambo,

I really felt excited when I read it. Now you have a problem with bugs on your teeth from riding with a big smile.

Ajays

Ajays wrote:Well done Krambo,

I really felt excited when I read it. Now you have a problem with bugs on your teeth from riding with a big smile.

Ajays

lol@Ajays - bugs on my teeth I can live with

Well done Krambo persistence and method paid off great result and you certainly know the bike much better than before.
Regards,
K-BIKE

The old K passed her MOT with flying colours today (21/11/2011) so now all I have left to do is to refit all the plastics/fairing parts etc. Thanks again to all here that helped me through the whole process

woohoo nice one !!

Against my better judgement I decided to refit all the plastics/fairings etc. this afternoon, replacing with new all screws/spring clips etc. as I went along so the bike is now complete once again and looking good - more importantly she is is still running well. The only downside now is that she has a red fuel tank (replacement) in amongst all the silver livery which looks a bit odd. I plan to get the tank sprayed to match fairly soon

Well done Krambo, I've been following the thread with interest and can imagine the sence of achievement you must surely be feeling. Enjoy the test runs ;-)

88KE wrote:Well done Krambo, I've been following the thread with interest and can imagine the sence of achievement you must surely be feeling. Enjoy the test runs ;-)

Thanks for that 88KE - hopefully someone that comes along after me will find something useful out of this lengthy thread. It has seemed like a huge mountain to climb and at some points along the way I ran low on oxygen - lol. However, I can't help feeling a great sense of achievement now I am at the summit (maybe temporarily). Thanks once again to all forum members that helped me along the way

i agree 88... good work krambo

sweet!!!

Krambo that is a sweet set of wheels and that high you are feeling now that its all sorted is what we all ache for. - congrats. Keith

Nice ride krambo!

Wouldn't it be easier to leave the tank alone and paint the rest red

I thought I told you before Blakey..... We don't want Wombats in the Northern Hemisphere!

blakey wrote:Nice ride krambo!

Wouldn't it be easier to leave the tank alone and paint the rest red

@blakey You are the second person that has suggested that so far but a). I don't like red ! (sorry) and b). It is listed on the registration documents as silver and I can't be bothered to change all the details with DVLA (Driver & Vehicle Licensing Agency)

Re the part that was fitted to the TB rail in front of the FPR. That is a vacuum switch that was only fitted on the early K's for fuel control. It gave a signal to the ECU (IIRC it was for better fuel mileage when in middle revs). it was quickly taken of, as it resulted in little. If you have it you also should have a 'vacuum hose' from that switch to the No 1 TB, same like the one from TB No 4 going to the FPR.

Good one you have her going again!!

ReneZ wrote:Re the part that was fitted to the TB rail in front of the FPR. That is a vacuum switch that was only fitted on the early K's for fuel control. It gave a signal to the ECU (IIRC it was for better fuel mileage when in middle revs). it was quickly taken of, as it resulted in little. If you have it you also should have a 'vacuum hose' from that switch to the No 1 TB, same like the one from TB No 4 going to the FPR.

Good one you have her going again!!

Thanks for that information ReneZ. My bike came off the production line in 1984 but was not registered until 1985 - that probably explains why this unit is present. My next question is this; if, as was the case here, the electrical connections were loose/hanging off this unit, would that have contributed to the original fault or can I assume that the FPR was in fact the culprit and that the loose connections on this other unit probably made little or no difference ? It does, as you rightly say have a vacuum pipe coming from it and going to No 1 throttle body which I am guessing could be blanked off.

Good question.....I don't know. I know of others who have it blanked off, just put a rubber stop on it as with the other 2 units and isolate the electrical connections. See if you notice a difference?

I don't consider that the wires hanging loose would have been part of your problem. Basically the vacuum switch would have grounded the signal wire when working, so occasional grounding of it should not be an issue; the bike is expected to run with the signal wire grounded or not.

Thanks for you valued input once again ReneZ - I guess I will leave well alone now that the old girl is running ok - taxed and insured her today so looking forward to a "legal" ride when weather and time permit

Good one you! Just visited your part of the country the last two days, would be happy to take the bike there!!