Greetings!!

I recently got my 85 k100rs back on the road with guidance from the amazing folks on this forum. It was running great for several weeks as I rode it daily and I went through a few tanks of gas. However, on the way to work today I ran into a problem. At the very end of my trip the bike felt like it was dying on me. It didnt stop running but it was moving very very slowly regardless of how much I throttled. Downshifting helped but I wasnt able to get it moving faster than a snails pace. I managed to crawl the final 1/4 mile to the parking lot and at the end the temperature light was flickering a bit as the bike struggled up a hill. 

I just went back to it after about 9 hours and its still not working correctly. The bike starts up fine, idles fine and when I throttle in neutral it sounds fine too. When I put it into gear and try to ride it just doesnt get going. When I throttle hard in first gear it sputters instead of accelerating.

My guess is that this is a bigger problem then my previous project of replacing oil/water seals. My intuition says it has something to do with not getting enough fuel but I am not sure how to check this or how to proceed from here. Any suggestions would be much appreciated!!

thank you all!

Ben

I think your diagnosis is correct - classic symptom of not enough fuel getting through. 

If you can get a pressure gauge into the line between the tank and fuel pressure regulator, that would be a start. 

Short of a fuel leak somewhere, which you would be likely to see, there is an intake filter in the tank, a metal can filter also in the tank, the fuel pump, yet again in the tank and the fuel pressure regulator (FPR) down near the injectors. Clogged filter or malfunctioning pump or FPR would cause the problem. There is a possibility that the injectors are clogged, but it's unlikely to happen to all four simultaneously, so one of the others is more likely. 

Bill

To add to Bills comment which I agree with on the injectors its possible to have a pipe disconnection inside the tank and which would not cause a leak. Run it with cap open and if you see petrol sloshing around from the pump but engine not running that may be your problem or it may be bad FPR. You seem to have enough fuel to start and to tick over but not to run which is suggesting low pressure.

Might sound daft but contaminated fuel can do that too, or diesel mixed in with petrol. But if sitting for a long time and now a few tanks of gas I would think change out the fuel filter.

Filter first then if it is still at it check the fuel pressure and go from there.

Thanks for all the info. Is there a way to determine if the filter is the culprit by looking at it before I purchase a new one? You all are the best!

Hi Benny,

the primary input filter is effectively a bag over the fuel intake, and that can be looked at, cleaned etc, no problem.

The other one is a metal can, so you might get a bit of an idea by trying to blow through it (in direction of fuel flow), but its not a very good indicator. Replace rather than attempt to clean.

If the primary filter is clogged, clean and try again. If still not good, replace the metal can one. Go on from there if necessary.



Bill

A new filter, if you blow air through it with your mouth in the direction of the arrow on the outside, feels like blowing through a straw. No resistance. I reckon if you remove the fuel cap assembly, gets your hand access to inside the tank, and the filter will be attached by stainless screwdown clamps. Undo both of the clamps and pull the filter off the hoses, then blow, don't suck, through the filter, see what it feels like. If you ve done that you may as well put a new one in anyway. Don't smoke and make sure the fuel cap assembly goes back on in the same direction as it came off. Cap opens back towards the rider and there is a little hole in the edge that lines up with a hole in the tank top for water/rain drainage I guess. 
This sounds like a problem I was having and my in tank fuel hoses were disintegrating, blocking the filter almost completely.
Don't be scared to have a go at this, there is plenty of help watching your progress.
Good luck mate.
RT

Ok I think I understand how to get started on this and what to look for. Thanks again for all the input. I'm gonna get it towed to my house today and take a look.

Do I need to siphon out the gas in there before removing the filter? There isnt much gas in there, probably 1/4 tank or less. I feel like I could probably just wear gloves and not get any gas on my hands or anything but I'm not sure if there will be a leak after I remove the filter(s).

Don't worry about the existing fuel in the tank - it can't go anywhere when you pull the pump and filter. Protective gloves are up to you

If you use latex gloves the fuel will melt them straight away.
Don't worry about draining the tank. For all the time your hand will be in there, won't do any harm.
I had a blocked filter and the bike completely died on me. Not able to blow through it when I took it out.

Ok got the filter out. It was pretty hard to blow through and the fuel that came out of the filter was black. Seems like the filter is worth replacing and might be causing the problem. Question though, should I replace the hose? Seems like I should as that might be disintegrating and causing the problem similar to what RT said. Also, there are bits of what I am assuming is the hose inside the tank. Should I be worried about that? I'll post some pictures of the tube and inside the tank in a few minutes, let me know what you think.

Thanks

Ben

If you do replace the fuel lines in the tank, they are rated SAE 30R10. This means that the fuel line can be fully immersed in fuel.

I have also just noticed that the crankcase breather hose is cracked and damaged. Can that be replaced easily? Could this be contributing to my problem?

Be

It does cause the bike to run rough. Cheap and easy fix.

blaKey wrote:If you do replace the fuel lines in the tank, they are rated SAE 30R10. This means that the fuel line can be fully immersed in fuel.

A new filter is a no-brainer. Any filter that is removed should be replaced with new unless you know the time and mileage history, IMHO. Ditto tank internal fuel hoses, but especially after your words on the filter and black stuff. 

Most parts places probably won't recognise the SAE reference, but they should be ok if you tell them that it has to be immersible in fuel. As blaKey says, they need to be, or the only question about problems is "when?"  

The picture of the bits in the tank doesn't seem to show a lot. If that's representative of the tank, and the pre-screen filter is ok and clean, I wouldn't worry.

Bill

Sounds like it's the worse for wear.
If you don't know when the filter was last replaced then fit a new one. the fuel lins will almost certainly need replacingand the crankcase breather.  Check the clamps on the throttle body rubbers, top and bottom, and you may even need new manifold stubs as they split and leak air. All the parts between the air filter and cylinder head are prone to air leaks as they age and that will effect the running.

While you are in the tank, whip the pump out of its holder.
It will only take seconds to do. Squeeze the clips and pull it out.
There's a nylon gauze filter on the end of the pump that can disintegrate and allow crap into the pump and seize it up.
Been there, done that.

thanks for the info blakey and bill. Rick- the throttle body rubbers and manifold stubs seem ok, not splitting or cracking...yet. 

I took out the fuel pump (see pic) and I seem to have found the cause of all the black bits in the tank and probably what clogged up the can filter. The vibration damper is completely shot and in pieces. There were even some large pieces of rubber at the bottom of the primary filter and a pile of smaller stuff below the filter under the pump. 



I can't thank everyone enough for their help and guidance on this- I am learning so much. Heres what I'm thinking based on everyones input and what I've seen:

Since the bike was starting and running at very low speeds I think the pump itself is ok. However, the primary filter and can filter were clogged and the crankcase breather hose was busted, each of which contributed to my inability to accelerate and sputtering when trying to do so. Does this sound accurate to everyone?

Ive read through previous posts about the crankcase breather and vibration damper and understand how to change them out. Wow is that damper expensive though on max bmw (as so many have pointed out). 

What I'm planning to do:

I want to replace the vibration damper, can filter and crankcase breather tube. Is it ok to purchase the following from beamer boneyard?  It makes me a little nervous that they are cheaper and not from bmw. 

Can Filter
Fuel Hose

Also, I'm confused about the vibration damper. Mine has 6 screws and a round shape (see pic below) while the new damper has 5 screws and a one flat side (see links below). Is this just a new design? I actually found the same design as mine on motobins, should I just get that one?


pre 85 vibration damper



 

I'm ready to purchase some parts but want to hear what you think first. 

Thanks again for all the help

Ben

Try EME always worth a look http://www.euromotoelectrics.com/BMW-K-Parts-s/60.htm?searching=Y&sort=13&cat=60&show=20&page=1

Beemer boneyard says in the description that everything pictured except for the ring will be shipped. That means you'll have to repurpose your original ring since you don't receive a new ring. That shouldn't be a fitment problem then. The picture of your old ring looks ok so you should not need a new one; just the rubber vibration damper.

I actually found all the parts I need for a a bit cheaper on motobins. Is there any reason I shouldnt purchase those?

Sorry for the basic question but I'm only just learning about all the places to buy parts. So far I know of maxbmw, motobins, euromotoelectrics, beemerboneyard and of course ebay/craigslist for used parts. I read a few previous posts about motobins and it seems like a good place to buy from, just want to be sure.

Ben

A large number of forum members, many not in UK, buy from motobins. They wouldn't keep doing it if they were no good. Go for it.

Bill

try http://www.motorworks.co.uk. For a lot of things they are a lot cheaper than motobins, plus they do a good pre-loved/breaking/wreckers/secondhand/call-it-what-you-like section as well.

Thanks again for all the help and information on this. After considering all the input I replaced the fuel filter, put in new connecting hoses, replaced the vibration damper and replaced the crankcase breather tube. After doing all this the bike was running great!.....for about a week.

Just when I thought I was in the clear and was about to thank everyone on this forum, the same problem seemed to occur yesterday. This time I was able to get going a bit faster then before, but the bike was struggling to accelerate again. I removed the new fuel filter just now and it is difficult to blow through. Not quite as difficult to blow through as the previous one I replaced, but definitely blocked way more than it should be after just a week of use. Being a bit less blocked then the previous one also explains why I was able to get going a bit faster.

I am going to replace the fuel filter again, but whats the problem??

My thought is that I am paying the price for letting the bike sit too long. The old vibration damper had begun to disintegrate resulting in rubber inside the tank. While I still have the mesh filter over the pump, maybe small particles are getting through and clogging the fuel filter? Should I just siphon out all the gas and as much of the rubber as I can and hope for the best? Or does someone think there may be something else going on?

thanks for considering this for me. I look forward to some additional ideas!

Ben

Hi Ben,
It seems to me that you should be able to give the tank a fair visual inspection to determine the extent of contamination inside.  What do you see in there?  I'd go well beyond siphoning the fuel out.  I'd remove the tank if it were mine and invert it to drain all the fuel.  Following that, a good flush would be in order. 
Don't discount the possibility that you inadvertently bought some poor quality fuel during the week.  That's not out of the question, especially if the interior of the tank appears relatively clean.

Agree. Take the tank off and empty it right out and flush. From your photos it looks like you have old rubber bits floating around. These will only break down over time continually clogging the fuel filter. Change the vibration damper and internal hoses and get all the crap out of the tank.

I've just done a routine filter change and was surprised to find bits floating around in the tank as I'd cleaned it out about a year ago. Took the pump out and the damper is starting to disintergrate. I drained the old filter into a glass jar and there was A LOT of black rubber fines that had made its way thru the pre-filter.

Thanks for the replies. Your past problem sounds very similar to mine, Kaptain Holister.

I have removed the fuel tank before so I am familiar with that process, but how does one "flush" the tank? Just pour more gas in and swish it around while trying to get all the black bits towards one of the holes?

thanks,

Ben

When the red light comes on you'll have about 6 or so litres in the tank. Remove the filler cap completely and give it a good slosh around and up-end the tank over a large clean basin/bucket. You'll need to shake it a bit to get the last of the fuel out over the lip on the inside of the filler hole. The crap will settle to the bottom of the basin. Just use a clean jar or cup to put about a litre back in and repeat.

Last year I had a sludgey coating over the bottom of my tank so I scrubbed what I could get to with a soft dish brush and a spray of carby cleaner.

Check the waste fuel for water. Could mean leaky filler gasket or blocked water drain hole.