Author Topic: Bringing K75 back from the dead.  (Read 2233 times)

Offline Sopp

  • Motobrick Curious
  • Posts: 16
Bringing K75 back from the dead.
« on: May 06, 2019, 05:07:49 PM »
Hereís the story: stolen, recovered, sold at auction, previous owner lost paperwork, I bought for parts, now I want to save it.
Canít read the entire vin # but it starts out: WB1  057307146????
Appears to be early 90s.  Mileage 3956
Fire burned the fuel injection system so that has been removed and new manifold built and Weber carb added.
Problem: it starts, idles a couple seconds, revs up tp 6000 for a couple seconds ( with throttle closed ) and then dies. Chip has been removed from keyó-is that part of the problem? Someone suggested that to me but not sure about that idea.
Iíve built hot rods for the last 60 years, but Iím new to BMWs, and cycles in general. 
Thank you for any help that anyone can offer.
Sopp

OK, Johnny, rip me a new one.
  • In my yard
  • K75

Offline The Mighty Gryphon

  • ^ Quintessential Motobricker
  • Posts: 4621
Re: Bringing K75 back from the dead.
« Reply #1 on: May 06, 2019, 05:37:45 PM »
Welcome, sounds like you have a truly unique situation. 

First, there is no chip in the K bike key.  Second, there are very, very few people who have experience with running a brick with a carburetor, so you are going to be spending a lot of time in uncharted territory.

I suspect that excessive fuel pressure is flooding the engine.  Are you running the stock fuel pump in the tank with the fuel pressure regulator?  I would supply fuel to the carb by gravity from a bottle about a foot above the carb.  From there, you will be able to start tuning the carburetor to get the engine to run properly. 

Do you have the ECU connected?  I am not positive, but I think it has something to do with ignition timing.  Not sure if it's needed, but you might as well have it connected in the ignition circuitry.

That's about all I can offer right now.  Good luck and keep us advised with how and what you are seeing.
  • In my garage in Marilla, NY
  • '94 K75RT Mystic Red, '91K100RS White/Blue, '89 K100RS Special edition White/Blue
Current:
'94 K75RT "Ilsa, She Wolf of the SS"
'91 K100RS "Moby Brick Too
'89 K100RS SE

Offline Sopp

  • Motobrick Curious
  • Posts: 16
Re: Bringing K75 back from the dead.
« Reply #2 on: May 06, 2019, 06:50:52 PM »
Thank you for the quick response.

Stock fuel pump has been replaced with one that only makes about 4 to 6 psi.  The ecu is still in there. I carefully removed only things directly related to the fuel injection system.
No chip?  Hmmmm, something has been removed from the key right where a chip would be. Iíve seen questions in forums about making ignition work without original key that had a chip. Hmmm.

I never build anything that is normal. Couple years ago I built the first and only hot rod completely wrapped in denim, no paint, just real denim material.

Not that it matters to this particular question, but this K75 is now a BMW Trike. Iíve added the independent rear suspension from a BMW 318i to it. Not even close to being done, but is ready to ride if I can get the engine to run properly.

Thanks again for any help.
Sopp
  • In my yard
  • K75

Offline Laitch

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Re: Bringing K75 back from the dead.
« Reply #3 on: May 06, 2019, 07:02:18 PM »
The good news is there's no need for concern about its being either a motorcycle or a BMW. It's a fuel-injected auto engine mounted horizontally. It's managed more like my '97 Ford F250HD.  :2thumbup:   It seems like quite an undertaking, but with 60 years of engine experience, you should be able to sort through it, one way or the other. Check in with Motobrick member Roland. He was intending a similar conversion.
  • Along the Ridley in Vermont.
  • 1995 K75 72,000 miles
I wept because I had no radials until I met a man who had no splines.
https://tinyurl.com/RillRider

Offline The Mighty Gryphon

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Re: Bringing K75 back from the dead.
« Reply #4 on: May 06, 2019, 08:20:28 PM »
The keys are late 70's technology.  The fact that they fold makes them high tech.  I'm thinking what is missing is the fancy little BMW roundel that is imbedded in the key.

Can you post a photo of what you have.  It will help us understand what you're grappling with.
  • In my garage in Marilla, NY
  • '94 K75RT Mystic Red, '91K100RS White/Blue, '89 K100RS Special edition White/Blue
Current:
'94 K75RT "Ilsa, She Wolf of the SS"
'91 K100RS "Moby Brick Too
'89 K100RS SE

Offline Laitch

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Re: Bringing K75 back from the dead.
« Reply #5 on: May 06, 2019, 09:52:31 PM »
No chip?  Hmmmm, something has been removed from the key right where a chip would be. Iíve seen questions in forums about making ignition work without original key that had a chip. Hmmm.
There's no electronic chip in a K75 key and never was. Move on to converting the trike to chain drive.
  • Along the Ridley in Vermont.
  • 1995 K75 72,000 miles
I wept because I had no radials until I met a man who had no splines.
https://tinyurl.com/RillRider

Offline daveson

  • ^ SuperNatural Motobricker
  • Posts: 491
Re: Bringing K75 back from the dead.
« Reply #6 on: May 07, 2019, 07:46:24 AM »
Not all your symptoms match,  but sometimes if the earth is poor it travels through the accelerator cable,  which often results in full acceleration.  On bricks the computer denies fuel, and alters timing,  to prevent engine damage from over reving.

I think the tenth digit of your vin indicates that it's a 2001 model. I think the month and year are on your engine also.
  • Victoria, Australia
  • Current;'86 K100RT Past; '97 Yamaha V Star 650 Yamaha V Star

Offline Sopp

  • Motobrick Curious
  • Posts: 16
Re: Bringing K75 back from the dead.
« Reply #7 on: May 07, 2019, 04:27:33 PM »
Now THATíS interesting!!  Iíll check my grounds and the throttle cable.  I guess the ECU could shut the fuel pump off, and also change the timing since it might not be getting the correct info from the ď missing ď fuel injection system.

I will try to take a good picture of the vin and post it. Maybe someone will be able to decipher what the other digits are.

Thanks again,
Sopp
  • In my yard
  • K75

Offline daveson

  • ^ SuperNatural Motobricker
  • Posts: 491
Re: Bringing K75 back from the dead.
« Reply #8 on: May 07, 2019, 05:21:26 PM »
Feel the cable. Start it again. When it conks out,  feel if the cable is warm.

I would consider the lazy man's way out and put fuel injection back on, but I'll be watching your build with interest. :popcorm
  • Victoria, Australia
  • Current;'86 K100RT Past; '97 Yamaha V Star 650 Yamaha V Star

Offline Sopp

  • Motobrick Curious
  • Posts: 16
Re: Bringing K75 back from the dead.
« Reply #9 on: May 12, 2019, 01:21:32 AM »
Here are some pics to give you an idea of what Iím doing.  Maybe someone with more experience reading VIN numbers on BMWs can decipher this set of numbers.
* 1D854576-B99F-4FBD-8464-003A38E53B83.jpeg (72.15 kB . 768x576 - viewed 123 times)
* 1D854576-B99F-4FBD-8464-003A38E53B83.jpeg (72.15 kB . 768x576 - viewed 123 times)
* 1D854576-B99F-4FBD-8464-003A38E53B83.jpeg (72.15 kB . 768x576 - viewed 123 times)
* 1D854576-B99F-4FBD-8464-003A38E53B83.jpeg (72.15 kB . 768x576 - viewed 123 times)
* 1D854576-B99F-4FBD-8464-003A38E53B83.jpeg (72.15 kB . 768x576 - viewed 123 times)
Iíll have a chance to work on it tomorrow, and will check the throttle cable for temp change when I try to start it.
Thanks again,
Sopp
  • In my yard
  • K75

Offline JPaganel

  • ^ Proficient Motobricker
  • Posts: 184
Re: Bringing K75 back from the dead.
« Reply #10 on: May 12, 2019, 01:44:10 AM »
Problem: it starts, idles a couple seconds, revs up tp 6000 for a couple seconds ( with throttle closed ) and then dies.

Weber carb added.
Seems like the cause of the problem.  :giggles

Seriously, though. I've heard of maybe three people who converted a Brick to carburetors. I never could figure out why. I own BMWs precisely because they are the oldest bikes commonly available with fuel injection.

What you have is not a BMW problem. You have a carburetor problem, and, potentially, an intake problem. Things like this is why I hate carburetors.

Not all your symptoms match,  but sometimes if the earth is poor it travels through the accelerator cable,  which often results in full acceleration.
How would a bad ground accelerate a carbureted engine? You can't make it do 6000 RPM with just a timing change. And if there is no FI, timing is all that's left to control electronically. You can make it do that if you are dumping too much gas in or you have too much air coming in and the carb adds fuel to go with it.

Either the carb is wonky, or there is an air leak.
  • Minnesnowta
  • 1986 K100RT, 1996 R1100RS

Offline Laitch

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Re: Bringing K75 back from the dead.
« Reply #11 on: May 12, 2019, 04:22:38 AM »
Put the fuel injection system in that Rambler American; don't let it go to waste. :giggles
  • Along the Ridley in Vermont.
  • 1995 K75 72,000 miles
I wept because I had no radials until I met a man who had no splines.
https://tinyurl.com/RillRider

Offline daveson

  • ^ SuperNatural Motobricker
  • Posts: 491
Re: Bringing K75 back from the dead.
« Reply #12 on: May 12, 2019, 05:35:12 AM »
I'm new to working on bikes,  but I've seen this accelerator/earth problem on cars a few times over the years. If earth is poor it sometimes travels through the accelerator cable.  The high current and small cable diameter causes the outer nylon cover to heat up,  making the cable sticky.  When overcome it moves suddenly and quickly,  and might be too sticky to return. Since the fuel injection unit has been removed but not the ignition control unit,  I guess this gives whack a wide berth.

It might not be the problem in this case,  but this build has raised my eyebrow  :popcorm
  • Victoria, Australia
  • Current;'86 K100RT Past; '97 Yamaha V Star 650 Yamaha V Star

Offline daveson

  • ^ SuperNatural Motobricker
  • Posts: 491
Re: Bringing K75 back from the dead.
« Reply #13 on: May 12, 2019, 08:09:18 AM »
The VIN number:

The first digit, W stands for the country, in this case Germany, called West Germany, back in the days.
The second digit B, stands for the manufacturer, in this case BMW.
I recon if you googled it, you would probably find the other stuff.
  • Victoria, Australia
  • Current;'86 K100RT Past; '97 Yamaha V Star 650 Yamaha V Star

Offline The Mighty Gryphon

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Re: Bringing K75 back from the dead.
« Reply #14 on: May 12, 2019, 09:41:47 AM »
While you're out there, take a couple photos of the CARBURETOR AND HOW IT"S PLUMBED to the engine.  It might help us figure out what you're dealing with if we can see a bit more than you're working on a trike parked near a light blue automobile.
  • In my garage in Marilla, NY
  • '94 K75RT Mystic Red, '91K100RS White/Blue, '89 K100RS Special edition White/Blue
Current:
'94 K75RT "Ilsa, She Wolf of the SS"
'91 K100RS "Moby Brick Too
'89 K100RS SE

Offline billday

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Re: Bringing K75 back from the dead.
« Reply #15 on: May 12, 2019, 02:55:41 PM »
Just want to say, your trike looks very cool and I'm looking forward to following this thread.

And yes please show us your carb and manifold.
  • New York State, USA 10977
  • 1985 K100

Offline Sopp

  • Motobrick Curious
  • Posts: 16
Re: Bringing K75 back from the dead.
« Reply #16 on: May 12, 2019, 09:12:07 PM »
OK, I posted 5 different pictures of the bike, but it shows up on my iPad as the same picture 5 times.  Are the rest of you seeing 5 different pictures or the same one 5 times????

I checked the throttle cable for any heat change when starting the beast, no heat, not the problem.

Iím attaching 1 picture of the drawing that started this whole concept.
* 1F67A7AC-9818-4E91-93E9-28FF52BC41B5.jpeg (54.5 kB . 768x576 - viewed 106 times)

I got it to idle for about 10 seconds today before it revved up to 8000 and then shut down. Next step will be to pull a good carb off of some other vehicle and try that. I think a Holley 2110 off one of my Ford Flatheads will work.
Fuel injection burned up, so putting that back on is not an option, other than buying a new system on line.

* 1F67A7AC-9818-4E91-93E9-28FF52BC41B5.jpeg (54.5 kB . 768x576 - viewed 106 times)
Iíll keep you posted on my progress
Sopp
  • In my yard
  • K75

Offline The Mighty Gryphon

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Re: Bringing K75 back from the dead.
« Reply #17 on: May 12, 2019, 09:36:32 PM »
I only saw the first photo in each post repeated. 

I have no idea on how your engine fuel and ignition systems are put together, but quitting at 8,000 rpm sounds a lot like the rev limiter kicking in. 

As far as the engine revving to red line, are you absolutely sure the throttle butterly is closed when the engine is running away???   It takes a fair bit of air(and fuel) to get to 8,000 rpm, and that much air isn't going to get past a closed throttle.  Take the air filter off and start the engine.  When it starts to run away, slap a towel over the the carb's throat to close it off.  Do the rpm's drop, or does the engine continue to run away?
  • In my garage in Marilla, NY
  • '94 K75RT Mystic Red, '91K100RS White/Blue, '89 K100RS Special edition White/Blue
Current:
'94 K75RT "Ilsa, She Wolf of the SS"
'91 K100RS "Moby Brick Too
'89 K100RS SE

Offline JPaganel

  • ^ Proficient Motobricker
  • Posts: 184
Re: Bringing K75 back from the dead.
« Reply #18 on: May 13, 2019, 12:23:47 AM »
It takes a fair bit of air(and fuel) to get to 8,000 rpm, and that much air isn't going to get past a closed throttle. 

Either the carb is wonky, or there is an air leak.
  • Minnesnowta
  • 1986 K100RT, 1996 R1100RS

Offline JPaganel

  • ^ Proficient Motobricker
  • Posts: 184
Re: Bringing K75 back from the dead.
« Reply #19 on: May 13, 2019, 12:26:47 AM »
Fuel injection burned up, so putting that back on is not an option, other than buying a new system on line.

Personally, I would have been looking into going forward to a more modern custom FI system rather than back to carbs.

I am sitting here rather seriously considering converting a 50cc moped to EFI. Already have the electronics and everything.
  • Minnesnowta
  • 1986 K100RT, 1996 R1100RS

Offline daveson

  • ^ SuperNatural Motobricker
  • Posts: 491
Re: Bringing K75 back from the dead.
« Reply #20 on: May 13, 2019, 01:48:27 AM »
Hey Sopp,

I love the Fred Flintstone look of your bike, the Carby that is.  :popcorm
  • Victoria, Australia
  • Current;'86 K100RT Past; '97 Yamaha V Star 650 Yamaha V Star

Offline Laitch

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Re: Bringing K75 back from the dead.
« Reply #21 on: May 13, 2019, 01:51:58 AM »
  • Along the Ridley in Vermont.
  • 1995 K75 72,000 miles
I wept because I had no radials until I met a man who had no splines.
https://tinyurl.com/RillRider

Offline daveson

  • ^ SuperNatural Motobricker
  • Posts: 491
Re: Bringing K75 back from the dead.
« Reply #22 on: May 13, 2019, 01:55:47 AM »
 :popcorm
  • Victoria, Australia
  • Current;'86 K100RT Past; '97 Yamaha V Star 650 Yamaha V Star

Offline Sopp

  • Motobrick Curious
  • Posts: 16
Re: Bringing K75 back from the dead.
« Reply #23 on: May 13, 2019, 02:21:06 AM »
The reason I like carbs is the same reason I canít seem to post more than one picture at a time........Iím OLDER than dirt.
Here is the one I tried to post with the previous post  [ Invalid Attachment ]
Iím trying to go retro with the bike.  If I donít go with the fender skirts, it will get 1935 Ford wire wheels.

Throttle plates are closed when it revs up.  Canít find any place that air is getting into the system.  Iím really baffled.  Iíll try a different carb tomorrow.

Is anyone seeing ďallĒ the pictures Iím posting or just the repeated pictures that I see?
Thank you for your patience.
Sopp
  • In my yard
  • K75

Offline Laitch

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Re: Bringing K75 back from the dead.
« Reply #24 on: May 13, 2019, 02:33:26 AM »
Is anyone seeing ďallĒ the pictures Iím posting or just the repeated pictures that I see?
You've posted five identical images of the trike and the Rambler, two identical images of the fuel tank and carb on the right side of the moto and one upside downóor maybe right side upóimage of something.

Post a photo of the intake manifold on the cylinder head.
  • Along the Ridley in Vermont.
  • 1995 K75 72,000 miles
I wept because I had no radials until I met a man who had no splines.
https://tinyurl.com/RillRider

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