BMW motorcycle trouble

Reece · 12-20-09, 06:11 AM

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 · 12-20-09, 08:42 AM

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 · 12-20-09, 08:56 AM

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 · 12-20-09, 09:41 AM

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 · 12-20-09, 09:56 AM

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 · 12-20-09, 10:06 AM

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 · 12-20-09, 10:31 AM

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.

12-20-09, 06:11 AM	#1
Reece CINC Pacific Fleet Join Date: Sep 2003 Location: Down Under Posts: 34,691 Downloads: 171 Uploads: 0	BMW motorcycle trouble 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. __________________ *Sub captains go down with their ship!*

12-20-09, 08:56 AM	#3
Reece CINC Pacific Fleet Join Date: Sep 2003 Location: Down Under Posts: 34,691 Downloads: 171 Uploads: 0	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! __________________ *Sub captains go down with their ship!*

12-20-09, 09:41 AM	#4
Letum Navy Seal Join Date: Feb 2005 Location: York - UK Posts: 6,079 Downloads: 43 Uploads: 0	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. __________________

12-20-09, 10:06 AM	#6
Onkel Neal Born to Run Silent Join Date: Jan 1997 Location: Cougar Trap, Texas Posts: 21,383 Downloads: 541 Uploads: 224	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. __________________ SUBSIM - 26 Years on the Web

12-20-09, 10:31 AM	#7
CaptainHaplo Silent Hunter Join Date: Apr 2007 Posts: 4,404 Downloads: 29 Uploads: 0	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. __________________ Good Hunting! Captain Haplo

12-20-09, 08:42 AM	#2
Catfish Dipped Squirrel Operative Join Date: Sep 2001 Location: ..where the ocean meets the sky Posts: 17,765 Downloads: 38 Uploads: 0	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

12-20-09, 09:56 AM	#5
Catfish Dipped Squirrel Operative Join Date: Sep 2001 Location: ..where the ocean meets the sky Posts: 17,765 Downloads: 38 Uploads: 0	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

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