Dear bikers,

On the road for 16 months already (Switzerland to Singapore) I am stuck in India because I believe a fuel/air system problem in my 1985 K100 RS. The problem appears randomly and mainly in low rpm. When I open the throtle the bikes doesn't answer or does a "break" and only several seconds later, suddenly, it starts to accelerate. The bike is running with very low power but maybe because we are above 3'000 m and didn't install an altitude plug (yet) on it.

I have checked the sparks and air filter. The pump is only 1 year old but it does a weird noise sometimes but seems to work correctly (test on battery).

Please advice where I can/should start searching for the faulty part.
Thanks in advance.

It may be intermittent power to the fuel pump.  You can jump power to the fuel pump by running wires under the gas cap.  The smaller diameter terminal on the fuel pump is 12V and the larger diameter terminal is ground. (If you do this of course be careful not to generate sparks in the gas tank.)

If the connector to the 85 tank is bad you can replace it with the white connector for the alarm system found in the relay box.

Clogged fuel filter maybe? After removing fuel cap try to connect fuel line directly without filter and look what happens?

nino wrote:Clogged fuel filter maybe? After removing fuel cap try to connect fuel line directly without filter and look what happens?

+1  Also possible water in fuel.  The fuel in India is not of the best quality. 

I would avoid bypassing the fuel filter.  If there is enough crap in the fuel to clog the filter, running around it WILL BE DISASTROUS.

If you suspect a bad fuel filter then you can pull it out (easiest when the tank is low) and try to blow through it. It should be fairly easy to blow through.

In addition to the above checks, be certain your battery's connections are clean and tight, your battery's ground connection on the transmission is clean and tight, that all fuel hose connections within the tank are tight, that the hoses within the tank aren't split and that your fuel pump hasn't slipped downward in its holder and is bottoming out on the floor of the fuel tank. That will intermittently block fuel uptake.

Thanks for the replies. Indeed, the fuel in India is the worst we had so far. I don't know what they put inside but honestly since we are in India we only encounter fuel problems in both bikes (Bonneville and K100).

I am going to check all these points you suggest and come back with the answer. The most frustrating is that we don't know when the problem will be generated... so diagnostic is hard. 

The high-pressure fuel filter is only 3'000 km and the tank is surprisingly clean.
What about the air intake, flowmeter...? Any ideas for that?

If you got a load of dirty fuel the filter will have filtered nearly all of it in the first hour or so of running do to the high flow from the pump that is recirculated back to the tank.  When you look in the tank all you will see is the filtered fuel, not the crap you put in.  

Look in the tank when the fuel pump is running and see if any fuel is coming out of the fuel line connections at the pump and the filter.  A plugged filter will raise the pressure to the maximum, about 65 psi if I recall.  That is enough to pop a hose off or at least cause a leak in the tank.

AmaiaUSC wrote:
What about the air intake, flowmeter...? Any ideas for that?

Finish one line of investigation before starting a different one.

You seem to have indicated you checked the spark plugs. What color were the spark plugs' electrodes—white, tan, grey, black? Was there residue of ash or oil? If the plugs smell like fuel, the altitude might be causing over-fueling so the altitude plug or manual connection of the wires that enter that plug's socket might be necessary to restore a balanced mixture and the power it would provide.

I am back with some pictures and statements after spending a couple of hours searching for something conclusive. In my opinion, there are many parts I should replace but not must replace regarding the problem described above. I took some pictures for you.

What I did, 
-I flushed in the opposite direction of the flow of the high-pressure filter. The fuel wasn't very dirty.
-I checked if the fuel was coming back to the tank from the rail. OK. 
-I checked all the electrical connections. All correct except I have now a doubt regarding the pump connector: it's 4 pins or 5 pins? I attached a picture.
-I recheck the spark plug. Thus 475 km after the last time I cleaned. They are completely black again, dry black deposit. I cleaned them again.

What I found,
- Black spark plugs. The mixture is no correct that's a fact. The throttle bodies where synchronized and spark plugs replaced 3'300 km ago. 
-Fuel pump strainer and support are not in good shape. Should replace them asap.
-Small crack in fuel hoose (out tank->rail). I think is not an issue so far. 
-Exhaust cracked. 4 to 1 area. Should weld asap.

Anything that seems obvious to you?

Bike starts very well and I will go for a ride tomorrow (altitude less than 2'000 m) and see if the problem still persists. If yes (which I think it will), I will much appreciate your answer as I need to find the issue to resume my travel. This bike was never released in India so the BMW dealer is useless in this case. I can only purchase parts from them; they import them from Europe and it takes between 2-3 weeks. What struggle me is not the lack of power in high altitude but those acceleration breaks... 

Thanks in advance for all your help, I really appreciate it!

Hi, last time I had black deposits on spark plugs problem was fuel pressure regulator. Result - too high pressure, much more than 2,5 bars.
It could explain running problems. Too much fuel in system choke the engine. Maybe you can find adjustable fuel pressure regulator.
Best regards

nino wrote:Hi, last time I had black deposits on spark plugs problem was fuel pressure regulator. Result - too high pressure, much more than 2,5 bars.
It could explain running problems. Too much fuel in system choke the engine. 
Best regards

Dear Nino, I was actually reading in the manual how to run a pressure test when I saw your message! This could explain the problem. I will check asap I got to Delhi and can find parts to run a test. I will keep you posted. Thanks.

AmaiaUSC wrote:The bike is running with very low power but maybe because we are above 3'000 m and didn't install an altitude plug (yet) on it.

AmaiaUSC wrote:What struggle me is not the lack of power in high altitude but those acceleration breaks...

I could use some clarity here. Do you mean that your engine has very low power but that doesn't bother you? That would bother me. An overly rich mixture causes intermittent stumbling, stalling and lack of power. It can be caused by a defective fuel pressure regulator or oxygen starvation at high altitude, among other reasons.

Disconnect the fuel pressure regulator hose at throttle body #4 and check it for presence of fuel after cranking the engine.

Or damaged vacuum pipe between throttle bodies and fuel pressure regulator..

Laitch wrote:

AmaiaUSC wrote:The bike is running with very low power but maybe because we are above 3'000 m and didn't install an altitude plug (yet) on it.

AmaiaUSC wrote:What struggle me is not the lack of power in high altitude but those acceleration breaks...

I could use some clarity here. Do you mean that your engine has very low power but that doesn't bother you? That would bother me. An overly rich mixture causes intermittent stumbling, stalling and lack of power. It can be caused by a defective fuel pressure regulator or oxygen starvation at high altitude, among other reasons.

Disconnect the fuel pressure regulator hose at throttle body #4 and check it for presence of fuel after cranking the engine

I see your point but once again, now I know it's not about the altitude because I am back from the mountains. I knew the bike struggled because the thin air, also me, by the way  It's not perfect but I can deal with the loss of power as is only punctual. 
What I need to know is the origin of the breaks. But like everyone seems to point to the same direction, now I need to check that dam pressure regulator asap. 
I will update the case as soon as I get to do the test you suggested.

Black soot on the plugs could also be the result of poor fuel quality.  I wouldn't be surprised if there were traces of diesel or paraffin in the fuel there.  If all else checks good, you may want to try a test run with a plug one heat range hotter to help burn off the soot.

The test run might be for one tank of fuel.  Pull the plugs and check them for color.  If good, then continue on with them, and be sure to check again when your travels take you to a part of the world with better refining capability.  Remember that you are looking for a nice tan color, if they are bright white, then there is a danger of pre-ignition which could damage the engine.

If the line from the FPR collapses on the bend where it goes back into the tank it will cause rich running and can cause weird noises from the fuel pump. Non OEM hoses are more prone to collapsing and delaminating on the bend. It can also be hard to detect as when you pull the tank back to check they can go back to the correct shape. Heat is also a contributing factor as the hose can soften. A good quality hose along with fitting a Unicoil can fix the problem.
Regards Martin.

Connect a hose to the front barb on the tank.  Can you blow air into the tank? Sometimes there is a valve there,  if blocked or partially blocked it could cause high fuel pressure.

You might hear dirt tumbling around when you blow, which might make it intermittent.

Your fuel pump plug is four pin.

Adding to Martin's comments:.

I have had fuel issues which seem fixed now

I replaced my fuel pressure regulator with an old one. Difficult for you but one could be sent. I do have a third if you want to try this...though Australia to whereever you are in India might be interesting.

I had (and retained) a spring above the FPR to ensure that the hose does not fold. So I recommend this.

There is a small vacuum hose going from the bottom of the FPR to #4 throttle body. Maybe check this.

Split hose?? - external fuel hoses are made up of 2 layers. The internal layer is fuel proof. You might only have a split in the outer layer. If it is not leaking it should be fine but do replace it as some stage (5/16 diameter).

Firmly fasten the fuel hose clamps using a 7mm socket NOT that stupid screwdriver.

Are you sure all hoses in the tank are good? If the fuel can be drained check them for splits. This is submersible line ("in tank fuel line... 5/16)... harder to get. I had 2 splits right next to clamps - so you can/maybe able to cut the split section out and shorten the line as a temporary move. You could use external line inside the tank as a temporary move if needed ... it will dissolve in time (not sure how long though ... a current project of mine)

Ah ... a breakdown in the middle of nowhere. It's all part of the thrill of travel isn't it. 

Good luck with it all

GF

I finally find a pressure gage /gauge (called it as you want) in crazy Delhi! Either BMW dealer, either Triumph, either Bosch service center had one, can you believe that? Then I went through those crazy bazaars with my schema but nobody apparently had the parts for running what I think, a simple test.

But today was the day, and find this old mechanic (yes, you can imagine the Indian cliché thus a turban man ) with a lot of tools. We ran the test, and my regulator is fine. We had a nice chat and he agreed to say that clearly, my bike is running too rich (black sparks). So, my problem is still there. I assume that my air filter and high pressure fuel filter are OK and I will now try to check the following parts who may be struggling:

-Fuel pump
-Throttle position sensor
-Air meter
-Engine compression

Does somebody know how to check the throttle position sensor and the air meter?

Thanks to all your messages and thanks to GF Wollongong for eventually sending a spare pressure regulator

AmaiaUSC wrote:-Fuel pump
-Throttle position sensor
-Air meter
-Engine compression

Does somebody know how to check the throttle position sensor and the air meter?
 regulator

This document has tests within it for many components. Add to your list the coolant temperature sensor. If it malfunctions, it can sometimes read engine temperature as cold when it is actually warm and that will lead to overfueling.

I agree, but clean the connector on coolant temperature first. It lives on dirty place under the radiator so its possible to send wrong signal. 
Nice to hear news from you. Best regards

Hey, that's a very useful document Laitch!
I will check the coolant connector, indeed is placed in a very dirty place.

I will keep you updated about my searches.
Cheers.

Make sure the big elbow between air flow meter and intake air box is properly fixed and is not split. A leak in that vacuum circuit and the synchronism between the throttles and the air flow meter is biaised. Then the calculator sends wrong amounts of fuel and the outcome is like a poor synchro....

According to the symptoms described in post Nr1, something wrong around the air flow meter is my favourite. Not sure of course.

A faulty temperature sensor is also a well known source of problems, but the engine "hesitation" before getting its power, as describled in the present case, is not logical then.

Testing that sensor (2500 ohm at 20°C and 175 ohm at 103°C according to my notes) will permit you to have your mind at ease with that.

I used to have a hesitation on acceleration, it turned out to be a worn out fuel pump, it was not giving the correct pressure.

Altitude adjustment...left in place?

Other than that I can't add to what's already been written.

Indian fuel is definately suspect - I know firsthand. See avatar.

have to agree Dai

either bad fuel or pressure line to injector issues ,
 not to discount a failing pressure regulator

if you can , make a t piece section with a pressure gauge, borrowed or whatever ,, and monitor the pressure on the feed line to the injector fuel rail  whilst the even is happening

could give new insight to fuel injector filter issues etc

good luck !

I am back from the workshop and news are not good.
So the pump and regulator seems to work fine after monitoring them with a fuel gauge.

So after this, I wanted to check the following parts as suggested by members: injectors, cooling temperature, throttle switch, airflow meter. But I ended removing the throttle body because of the 4th throttle body air bypass screws wasn't doing any change. So I suspected the problem there. So with the throttle bodies out, I just realized that cylinder 1 and 2 are leaking oil and 4 doesn't see to work (faulty injector may be the reason).  

I took a picture where you can see the deposit. So this is a quite bad new because I probably need to rebuild my piston rings in India and parts are not available. But there is something that doesn't match to me: why is there oil deposit in the throttle body but not in the sparks if pistons are leaking? 

Is that definately oil and not just carbon from a persistant misfire?

Dai wrote:Is that definately oil and not just carbon from a persistant misfire?

The deposit in the throttle bodies is wet, I am sure about it.
I will run a compression test tomorrow so I can be sure if rings need to be replaced.

Why misfire can happen?

Hi IF it is definitely wet oil then it could be the sump oil level was too high (overfilled) this could lead to oil passing through the crankcase breather and into the air filter box  then into throttle bodies.Failed piston rings would be heavy smoking loss of power and the spark plugs would be badly fouled Compression test will give best indication of the problem.Best of luck.

In which condition is the oil vapors recycling rubber pipe? The one behind the throttle switch, going from engine to air box.

It is a well known trouble maker if cracked or broken. If it is oily it is dead... Apparently, replacing it by an ordinary pipe is not ideal. I do not know why. Maybe the shape.

+1 with moriarti 

The closer the cylinder to the crankcase breather hose,  the worse the problem. Maybe too much oil, or coolant is entering the sump. If loosen the sump plug a little bit, does water come out? Amount of oil,  coolant or fuel used might give a hint. Or when removing oil filler plug is oil flinging around everywhere from crankshaft dipping in oil? Or blow by less likely. 

Why cylinder 4 misfire or not working, just too much oil fouled.

I run a compression test yesterday and news are the following: the engine is overall OK, just piston 2 was low in compression. After adding some oil in the intake valve, compression is back so I assume that the intake valve is not seating correctly. I thought to add some additive and try to clean the engine instead of disassembling all the engine for cleaning once the bike will be running again.

So the problem doesn't come from the engine. I removed all the throttle body and the airflow meter and... OH SHIT! Everything is FULL of super-thin dust. And when I say everything, is everything: like the tiny temperature sensor, was covered by dust. So I think, the problem is there. The origin? badly placed air-filter and I can only blame myself for this.

So now I am trying to clean carefully everything the best I can as a lot of things are very fragile. Put them back and run a test. Lucky us, we found a workshop where the guy has all the tools for hope, putting all back properly.

Finger crossed. I will keep you updated.

daveyson wrote:+1 with moriarti 

The closer the cylinder to the crankcase breather hose,  the worse the problem. Maybe too much oil, or coolant is entering the sump. If loosen the sump plug a little bit, does water come out? Amount of oil,  coolant or fuel used might give a hint. Or when removing oil filler plug is oil flinging around everywhere from crankshaft dipping in oil? Or blow by less likely. 

Why cylinder 4 misfire or not working, just too much oil fouled.

Still can not explain why there is oil in the throttle body. Piston 1 & 2 where the oiliest and they are the most away from the breather. Also, each cylinder have a pipe in the plenum chamber so if oil was arriving there, the level should go up before entering the throttle body I think.

AmaiaUSC wrote: OH SHIT! Everything is FULL of super-thin dust.

I really don't want to think what that dust is doing to the health of the people that have to live in it. Two days of riding through it and I had to replace a very expensive pair of spectacles (glasses). The dust did a really good job of sand-blasting the lenses.

As regards the oil: I've seen throttle bodies and carburetors like that for no apparent reason. I think you've found the cause of the msifire, so at this point I wouldn't be worrying too much about the TBs.

I know, I know... I am also concern about the health of my lungs after 6 months in India. 

Yep,  I was looking at that backwards, so hopefully just needs inlet cleaned.

AmaiaUSC wrote:So I think, the problem is there. The origin? badly placed air-filter and I can only blame myself for this.
Finger crossed. I will keep you updated.

How about updating us right now and explaining what you meant by "badly placed air-filter"?

Hello!

Some update after several ride test with the brick and I am happy to communicate that the bike seems fine again. Yeah!
So yes, I am afraid that the problem was caused by us: one of the lips of the air filter folded and the dust went into all the airbox causing a huge mess. 
After a good deep clean of the airbox and throttle bodies and some engine and fuel additives everything is back to normal and hope we can resume our trip to the east.

Thanks again to all of you for your help!