BMW motorcycle trouble

[Reece]

I have an old 1987 BMW K100 motorcycle, that runs rough!! actually not ridable!!
When I start and run up through the gears riding modestly all is ok, but once in top the bike holds it's own until I encounter a hill, naturally I have to apply more throttle but the bike does nothing, almost seems to die, if the hill is steep I may have to drop back a couple of gears, even on a straight if I try to accelerate the bike again refuses to respond, and if I open it out completely the power is really reduced and the revs drop and engine runs rough, can pull the clutch in and the engine revs are only around 1500 rpm, running very rough, if I slowly release the throttle the engine will recover and almost scream, if it had a carby I would suspect this but it is fuel injected, the fuel pump has been a little noisy even when tank is full lately, so I am wondering if this could be the problem or the filter, both are submerged at the bottom of the fuel tank and if I had to guess I'd say that it's probably original!!
Could the pump/filter cause this, if not any suggestions very welcome, trouble with bikes is getting access to parts, virtually have to strip it to do anything plus parts for a BMW are not cheap!
Thanks.
Edit: It is not likely to be plugs, leads, or injectors, since it's unlikely that all 4 would die at once.

[Catfish]

Magnetoes ? Is there enough (!) juice to feed the spark plugs ? And i do not mean "do they fire at all", but enough voltage and/or amperage at higher revs ?
Another idea is fuel pump ok, or the fuel filter/sieve clean ?
Good Luck ,
Catfish

[Reece]

No magnetos, it's like a standard fuel injected car of today, has Bosch alternator with 12v battery, the bike is 1000cc, 4 cylinder, but yes I suppose the coil could be stuffed, since it's electronic ignition could be computer or ignition system (another computer box), there are so many things that's why I'm hoping someone may have had this type of problem and knows the likely fix!! To me it seems like the engine is starving for fuel, a genuine BMW fuel pump is $250, (though I might try a generic brand), this gives an idea though of cost if I was to just try a hit or miss method!

[Letum]

The tiny holes, usually in the petrol tank cap that prevent a vacuum
forming can become blocked causing fuel supply issues. I have had that
problem before.
Although perhaps this isn't an issue without carbs.

[Catfish]

Hello,
well you can check your coil at a local garage, as well as the controller (regulator?) of the alternator.
So is it an alternator, or a dynamo ? Guess the latter ...

Usually here in Europe Bosch parts are a lot cheaper than BMW ones, but they are just the same - only the "BMW part" has a BMW logo imprinted on the Bosch part lol.

But i would first check the filters, and the fuel pump ... losing performance at higher revs, or load, is usually clogged/damaged fuel system or coil.
It could also be gas bubbles in the fuel lines, if there's a damaged heat shield.

I once had a french car, phantastic in winter and design, but with a german Bosch electronic ignition and fuel injection system. All the people always talked about bad french cars, but it was this Bosch ignition system that made it that unreliable. Since then i write it as "Boche", like swine .
It took me 3 months to find out what it was (black box ignition system), and the local Bosch dealer had not found it - but it's understood he took money for searching 4+ hours, 300 Euros or so.

Greetings,
Catfish

[Onkel Neal]

I agree with Catfish, replace the filter first, that's the cheapest to start with and filters should be replaced periodically any way. Also, check the fuel line, be sure it is not pinched. If that doesn't improve the performance greatly, then see if you can pull the fuel line and get a volume rate on the fuel pump, make sure it is supplying normal pressure and flow.

[CaptainHaplo]

Correct me if I am wrong, but your saying that it will reach full RPM's when you slowly throttle up, but if you twist the throttle she stutters? If this is the case, you are likely looking at the fuel pump. If it was fouled injectors, vacuum on the tank, dirty filter, pinched line, etc, it would do it consistently. But if a pump starts to die slowly, it can show up as no being able to swap speeds quickly.

[AVGWarhawk]

Other tell tale sign, is the engine when sputtering spewing black smoke as if the bike is running very rich? If it is blowing black smoke then you are getting enough fuel. If so, ignition problem. Do these bikes have timing advance and retard systems? If so, is the timing mechanism working correctly?

[Reece]

Letum said:
The tiny holes, usually in the petrol tank cap that prevent a vacuum
forming can become blocked causing fuel supply issues. I have had that
problem before.
Although perhaps this isn't an issue without carbs.

I did think of that so I stopped the bike, opened the cap, then started off again but the problem was there immediately!

Catfish said:
well you can check your coil at a local garage, as well as the controller (regulator?) of the alternator.
So is it an alternator, or a dynamo ? Guess the latter ...

The coil is a weird thing with a plug of a number of pins, typical computer controlled! the bike has a standard alternator.

Catfish said:
But i would first check the filters, and the fuel pump ... losing performance at higher revs, or load, is usually clogged/damaged fuel system or coil.
It could also be gas bubbles in the fuel lines, if there's a damaged heat shield.

Yes my guess would be pump/filter, not sure about the heat shield, what would the shield be protecting?

Neal said:
I agree with Catfish, replace the filter first, that's the cheapest to start with and filters should be replaced periodically any way. Also, check the fuel line, be sure it is not pinched. If that doesn't improve the performance greatly, then see if you can pull the fuel line and get a volume rate on the fuel pump, make sure it is supplying normal pressure and flow.

Yes I think the fuel pump/filter is the best guess, I did forget to mention that the fuel pump not only whines but makes a spitting sound, don't know if that's normal.

CaptainHaplo said:
Correct me if I am wrong, but your saying that it will reach full RPM's when you slowly throttle up, but if you twist the throttle she stutters? If this is the case, you are likely looking at the fuel pump. If it was fouled injectors, vacuum on the tank, dirty filter, pinched line, etc, it would do it consistently. But if a pump starts to die slowly, it can show up as no being able to swap speeds quickly.

Sort of, it's like it has a governor on it and only allows a certain amount of fuel through, if I exceed this by climbing a hill or accelerating past 80km or so then it fails to respond and if you open it right up you can hear the air intake roar so it's getting too much air for the small amount of fuel, well that's the best guess or description I can give, if I stop the bike in neutral it revs fine (no load).

AVGWarhawk said:
Other tell tale sign, is the engine when sputtering spewing black smoke as if the bike is running very rich? If it is blowing black smoke then you are getting enough fuel. If so, ignition problem. Do these bikes have timing advance and retard systems? If so, is the timing mechanism working correctly?

Ah that's a good question, no misfires or black smoke!! The advance/retard is controlled by the ignition computer box, but I think since it's not miss-firing that could be ruled out.
Well a big thanks for all the help, I do feel that I will have to empty the tank and remove/inspect the pump/filter as well as the lines, atleast this is easily accessible, will have to wait till after Christmas but it gives me a plan and eases my mind a little!
Cheers and happy Christmas to all.

[Reece]

Well now that Christmas is over I decided to remove the fuel pump and petrol filters, I don't know if this would cause the "starving for fuel" problem, opinions please? The first is the inlet filter that mounts on the pump itself:



This is the view of the outlet fuel filter, is it normal that it takes quite a bit of blowing pressure with mouth for air to go through?



Maybe the pump is ok! (hopeful!)

[DivingDuck]

Moin Reece,

I stronlgy recommend to change the inlet filter. Would be no bad idea to change the second filter as well. And yes, it´s normal that it takes some pressure to make the air go through as the flow is not unrestricted.

I had a similar problem once with my KTM. Allthough it has a carby, the symptoms are similar. At lower revs the bike went just fine. But whilst quickly accelerating the power was instantly gone and the engine even stopped. The cause of this trouble was a bended rubber fuel pipe. It allowed just enough fuel to pass through to run the engine at low to medium revs but nothing that needed some power. The original fuel pipe in question got pinched and was replaced by me. But when I replaced it, I missed to look into the tiny tube. To avoid kinking a tiny metal spring had been inserted. After extracting it from the original and pressing it into the new feed pipe, the bending just followed the expected 'U' and didn´t get twisted or kinked again. This lack of fuel flow however may explain the whining of your fuel pump. Imagine the fuel pump being managed by the computer. It calculates the needed amount of fuel in regard to air and powersetting, don´t know whether the old ones take other values into consideration as well, and starts spinning accordingly to "produce" some fuel. But there´s no fuel coming out of the feed pipe. What would you do, ... whine!

So, check the fuel supply and replace the filters. My 2 Eurocents,
DD

I'd just change the filter and hope for an improvement.
If that doesn't happen, my next step would be the pump.

My car just went through the same scenario, and it was the pump.

[Reece]

I will replace the 2 filters and try that, I just checked and the price for a new BMW pump is $400, if it causes more problems I will try out a generic fuel injected car fuel pump ($50), just noticed another device called a Pressure Regulator:

The fuel pump supplies pressurized fuel to the injectors at a constant pressure. The pressure regulator maintains a constant fuel pressure of 36psi, if the specified pressure is exceeded the pressure regulator valve opens, allowing the fuel to return automatically to the fuel tank via a separate hose.

I would doubt that this would cause a problem as it is for excessive pressure and in this case it would have to be low pressure, pity I don't have a pressure gauge to test the pump!

[Catfish]

Hi,
does the filter imprint say 06.06.84, or 94 ?
Be it 94 with 15 years of duty I would replace it anyway lol

Greetings,
Catfish

[Reece]

The pump only has:

Bosch 0 580 463 998
12v 014 546 Made in Germany.

However I think it's original, the bike is 23 years old.
Edit: I have read that this pump will do the job but don't know where I can get one:
NAPA Part Number: 2P74095
or:
Advance Auto Part Number: E-2042

Also Bosch 0 580 463 999 fits but I think this is just as expensive!!