BMW K bikes (Bricks)

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PNWK100

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Hey folks,

I'm working on getting an '85 K100 back up and running. It came to me disassembled but in good condition and "ran before it was disassembled".

I've recently wired up a Motogadget Motoscope Mini gauge (with "Combi" indicator lights) and their RFID mLock ignition. I did the daisy-chained 4 relay trick to get the neutral light to work. I used the supplied relay that came with the mLock ignition, pulled out the stock Bosch unit, and wired the new relay's ground into the ground terminal of the Bosch relay.

I've put everything back together to the best of my knowledge but I'm having starting issues. When I hit the starter button the starter gives me a half second bump/pulse every 1-2 seconds but doesn't fully turn over. The battery is fully charged and I've tried hooking up an engine-start jump pack that plugs into the wall. I still get the same bump/pulse action.

My questions:

1. What's the cause of the starter bumping but not turning over the motor?
2. Should the fuel pump be running in "accessory mode" like a car or only when the starter button is pressed?

    

robmack

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So, did you verify that it could run as a stock machine before you started your modifications? If not, it's now difficult to tell whether the problem has been introduced by the aftermarket stuff or whether it was a systemic problem with the motorcycle in the first place.

Are you powering the M.unit by a switched 12V supply independent of the LSR?


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PNWK100

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No I did not verify it ran prior because it was missing a lot including the key. I don't have the m.unit. If you mean the gauge yes, it's run off switched power (green black wire). What's LSR stand for?


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PNWK100

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Here's a video of it.

https://youtu.be/QQQhGhitav8

I'm holding the button down and the battery is connected to a 12V jump pack plugged into the wall.

    

robmack

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I was thinking m.unit instead of m.lock. Slipped up there.

LSR stands for load shed relay. It is a relay that cuts power to a number of unnecessary circuits on the bike when trying to start (for example headlights) so that the full power of the battery is available to the starter.

It sounds like power to the start relay is being interrupted. I take it the m.lock has replaced the ignition lock and that you've wired up the circuits so that they correctly emulate the ignition lock. If the m.lock is powered from switched 12V controlled by the LSR, then everything operates normally until you press the start button. The LSR immediately cuts power, the m.lock looses power and the start relay drops. I don't know for sure this is the problem though.

I'm confused by the description of the relays. I lose understanding of which relay is being spoken of and how they are wired up. Can you post a schematic to help?


The fuel pump is working properly (starts with the start button and runs on for 1.5 seconds after release) which means the FI relay and ICU is operating.


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Robert
1987 K75 @k75retro.blogspot.ca
2011 Moto Guzzi V7 Racer
http://k75retro.blogspot.ca/
    

PNWK100

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Did you watch the video? It does seem like the start circuit is being interupted. Notice in the video that the gauge resets as soon as the starter kicks. I just attampted to jump the starter directly from the jump pack and got a similar result. Something seems to be cutting power even when directly connected to the starter. Is that even possible or is the bike requiring much more CCA than it should for some reason?

Video of starter jump:

https://youtu.be/WDOcNMdB_fQ



Last edited by PNWK100 on Sun Jan 21, 2018 8:32 pm; edited 1 time in total

    

PNWK100

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The jump box I have is a 12V 55A engine start FYI


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1985 BMW K100
    

PNWK100

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Ok it's come to my attention that I mistook which stock relay did what and have clearly wired this incorrectly. Instead of getting real confusing and explaining what I did maybe it's best to start with what I should have done.

Here's the mLock wiring diagram:



How should I be wiring this in?
Do I use the supplied Motogadget relay or tap into an existing BMW relay?

Here's the K100 diagram for reference:


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1985 BMW K100
    

kioolt

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That video sounds like a dead battery to me even though you're using a jump box. Have you measured the voltage from the starter terminal to the starter body when trying to start it? That would actually me more then just about anything.


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2004 R1150RT 183,000 miles
1991 K100LT 128,700 miles
1982 R100RT 106,900 miles
Total418,600 BMW miles

AMA,BMWRA,BMWMOA


The cheapest thing on a BMW is the nut that connects the handlebars to the seat.
    

PNWK100

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@kioolt wrote:That video sounds like a dead battery to me even though you're using a jump box. Have you measured the voltage from the starter terminal to the starter body when trying to start it? That would actually me more then just about anything.

It was a misunderstanding on my part. I pulled the Load Shed Relay by mistake when wiring in the new motogadget relay. I just put the LSR back in and it cranks like it should. Now with the LSR back in the accessory power does not turn off with a second swipe of the RFID tag. It only switches off the motogadget relay.

Here's how I currently have it wired up:



Last edited by PNWK100 on Tue Jan 23, 2018 5:23 pm; edited 1 time in total


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1985 BMW K100
    

PNWK100

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Anyone? Could still use some help on the correct wiring.


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1985 BMW K100
    

PNWK100

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Update:

I sorted it out. Here's the correct mLock to K100 wiring if anyone needs it:


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