BMW K bikes (Bricks)

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LA_Cafe

LA_Cafe
New member
New member
First post, and have been searching on this topic to dead threads.

I have begun the build of my cafe project, starting from the front (Redoing all cables, handle bars, new levers, starting electronics, signals, etc)

Now that I have all of this complete and have begun my gauge install with a BEP 3.0 I wanted to fire the bike up to see where I am netting out.

New battery, fully tendered. Starter relay isn't welded, all seems right.

When I pull the choke and crank the bike, it runs, but the moment I let go of the starter button, she turns off.

I checked all of the problem areas 
- ECU (unplugged, contact spray, reseat)
- TCI (unplugged, contact spray, reseat)
- Tank connector, checked and double checked... seemed fine.... more to come
- Ignition switch is good

So after a lot of research with people that had the above check out I came to see that the LCD of most people's issues was inside the tank.

Took the fuel pump out, bench tested, and man is this thing loud... I am not hearing any of this when it's in the tank. So I put it back in, rewired everything, and opened the fuel sending line, and fuel was pumping out of it.

Then I decided to go to the base of the cause and disassemble the fuel tank connector

Come to find out that the float at some point of this bike's journey has rusted away and a previous owner just deleted it.

My current plan of action is to look at wiring the fuel pump up so that it gets a constant 12V when the ignition is pressed and the bike is on, and the 12V turns off if the kill switch it enabled or the ignition is turned off.

Any guidance?

Odd thing is that the bike ran before I took the tank off, although the tank did drop (butter fingers on my part, which I am wondering if it was the last straw for this shade tree setup)

I'd like to replace the aging wires inside the tank as well, are there specific fuel grade wiring that I should pick up?

I think this may be affecting more people and hope I can get this fixed and help more K riders out there.

Starts only while holding start button - Tracking down the cause Img-8010

    

robmack

robmack
Life time member
Life time member
Hi,

It helps a great deal to us attempting to provide guidance to include the model and year of your bike in your signature.  Based on previous posts, it appears that you have a later model K75.  Is that correct?

Since you mention that you've done some work on this bike, what would that work entail?  Is it just the addition of the BEP 3.0 and deletion of the OEM cluster?  Or has there been more?

The starter button when pressed, provides 12V to the starter relay as well as the ICU and ECU.  If the start button is released, power to pin 6 of the ICU is cut.  Your problem may be related to the quality of connections to the ECU and ICU.  I'd search those areas a bit more, making sure all connections are secure and solid.  Also check grounds especially the ones under the tank on the frame.  Make very sure that the ECU connector is pushed fully home.

P.S.  Please don't putz around with the FI circuitry until you get your bike working reliably with the OEM wiring.  It will be difficult to debug problems if you haven't made informed changes to that circuitry since the Jetronic system is complex.


__________________________________________________
Robert
1987 K75 @k75retro.blogspot.ca
http://k75retro.blogspot.ca/
    

indian036

indian036
Life time member
Life time member
I’d be wary of the pump wiring change you envisage. As far as I know, the pump electricity supply is dependent on a running engine apart from when it is being started.
If it will keep pumping while ignition is on and kill switch is off, if there is an incident where the engine stops and ignition is still on, then there will still be fuel circulating. Any opening in the fuel system that might result from an ‘off’ will mean that fuel will continue to be pumped out. The risk of a big fire will be high. 

Bill


__________________________________________________
1985 K100RT  VIN 0028991  My original Very Happy   (Historic rego)
1985 K100RT  VIN 0029036  BOB the Blue Old Bike  (Historic rego)
1990 K100LT  VIN 0190452  Work in progress
1984 K100RT  VIN 0023022  Work needing lots of progress

1986 K100RT  VIN 0090542  Work needing lots and lots of progress
1993 K1100LT  VIN 0183046  Work in progress
1993 K75S  VIN 0213045  Newest toy, slightly non-original
    

duck

duck
Life time member
Life time member
@indian036 wrote:I’d be wary of the pump wiring change you envisage. As far as I know, the pump electricity supply is dependent on a running engine apart from when it is being started.
If it will keep pumping while ignition is on and kill switch is off, if there is an incident where the engine stops and ignition is still on, then there will still be fuel circulating. Any opening in the fuel system that might result from an ‘off’ will mean that fuel will continue to be pumped out. The risk of a big fire will be high. 

Bill
From the wiring diagram it looks as though a ground signal from Pin 7 (Yellow/Brown wire) of the ICU is what triggers the fuel system relay.


__________________________________________________
Current stable:
86 Custom K100 (standard fairing, K75 Belly pan, Ceramic chromed engine covers, paralever)
K75 Frankenbrick (Paralever, K11 front end, hybrid ABS, K1100RS fairing, radial tires)
86 K75C Turbo w/ paralever
94 K1100RS
93 K1100LT (x2)
91 K1
93 K75S (K11 front end)
91 K75S (K1 front end)
14 Yamaha WR250R
http://www.ClassicKBikes.com
    

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