Author Topic: 1992 BMW K75S ABS Running Rough & Rich  (Read 948 times)

Offline ExpatAussieBrick

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #25 on: July 08, 2019, 12:16:45 PM »
Hey guys,

Bit of bad news after having a great weekend riding to the beach for the 4th of July and having a blast on the bike it decided to act up again yesterday after riding home from a dinner date riding two up. The usual thing it's been doing past few weeks I was at a stop light turned green gave it throttle went to pass the cars and suddenly it lost power and barely wanted to rev to 2000 rpms I gave it some more and the engine died and we coasted to a stop. Initially engine turned over but refused to start. Then after fiddling around with the connectors again it started and got us all the way home without much more trouble besides one more incident of bucking under throttle.

I'm thinking I will remove the tank this week and take a photo of all the connections under there and clean them all up. The problem does feel electrical because it's so intermittent and the fact that cleaning the 4 pin really helped. Also thinking about checking the crank case Z hose and the throttle position sensor. I want to be able to trust the bike again before taking it anywhere far from home or on heavy traffic roads.

Kinda feeling like putting it up on craigslist while I go about trying simple fixes for it. It's just too complex of a bike for me with no real garage space or place to work on it and i've spent too much money on it to start throwing parts at it. That being said i'm not giving up yet just giving myself options.

As a clue, I did pull the plugs again after the incident and they do look a little on the lean side for sure with a light coating of white dust.



  • New York
  • 1992 BMW K75S ABS

Online Filmcamera

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #26 on: July 08, 2019, 12:25:50 PM »
Sounds like a classic case of four pin connectors woes to me.  I have had the same thing a few times... in the end all I have to do is disconnect and reconnect the four pin and few times and everything is ok again. Have you tried cleaning the four pin connector with Deoxit or something similar?



  • San Jose, Costa Rica
  • 1991 K100RS 16v ABS1, 2018 Triumph Street Triple RS 765
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Offline The Mighty Gryphon

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #27 on: July 08, 2019, 12:36:59 PM »
I agree on the four pin tank connector.  A shot or two of Deoxit may clean it up enough to be somewhat more reliable. 

A few owners have had some success with gently pinching the pins in the male side of the connector to ovalize them slightly so they make better contact.  Others have just replaced the connector with an SAE 4 pin trailer connector, a job that requires you be sort of handy with crimping butt splices or a soldering iron.
  • In my garage in Marilla, NY
  • '94 K75RT Mystic Red, '91K100RS White/Blue
Current:
'94 K75RT "Ilsa, She Wolf of the SS"
'91 K100RS "Moby Brick Too

Offline ExpatAussieBrick

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #28 on: July 08, 2019, 12:39:48 PM »
I sprayed the crap out of it with deoxit last night and reconnected as tight as possible. Will see how it goes today might take it for a short ride.
  • New York
  • 1992 BMW K75S ABS

Offline Martin

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #29 on: July 08, 2019, 01:47:02 PM »
I found that my 4 pin started playing up after 20 years of no problems. Sprayed it with the 2 part DeoxIT a couple of times which temporarily solved the problem. It broke down again in front of a electrical supply shop which I took as a sign that I should replace the connector. I went in and bought a waterproof connector $20.00 Au and no problems since.
Regards Martin.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline Scott

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #30 on: July 08, 2019, 04:18:39 PM »
I've never had a problem with my 4 pin connector......yet, but is it a problem with the physical contact of the sockets and pins, or an oxidation problem that can be solved with deoxit or similar?   It certainly could be a more robust connector.  cheers.
  • SoCal
  • bmw R100r, bmw k75, hondapotamus G/W, XT 500 enduro

Offline The Mighty Gryphon

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #31 on: July 09, 2019, 10:05:58 AM »
Every time I take mine apart, I wonder if I am breaking the connections in the plug body between the wire and the contacts.  The latching tabs are so big and hard to disengage that I have to pull pretty hard on the damn wires to get it apart.  On at least one bike I have filed down the dogs that the lock the connector halves together to make it easier to pull apart.

A little Vaseline smeared on the mating surfaces also helps make it easier to get the connector apart.
  • In my garage in Marilla, NY
  • '94 K75RT Mystic Red, '91K100RS White/Blue
Current:
'94 K75RT "Ilsa, She Wolf of the SS"
'91 K100RS "Moby Brick Too

Offline Martin

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #32 on: July 09, 2019, 01:58:33 PM »
Even with fitting a new waterproof connector I try to avoid disconnecting it. That's the reason why I pull the #6 fuse and not the pump connection when disabling the fuel pump.
Regards Martin.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline John Lang

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #33 on: July 09, 2019, 07:22:59 PM »
To get the 4-pin plug apart, try sliding the jaws of a needle nose pliers between the locking tabs and the central body of the plug, bending both tabs back simultaneously until they disengage. Then squeeze the pliers gently to grab the removable part of the connector while lifting it away from the rest of the plug. Works for me.
  • Ottawa, ON Canada
  • 1987 K75C

Offline ExpatAussieBrick

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #34 on: July 11, 2019, 12:42:46 AM »
Hey guys,

Some more unfortunate news so I had a go at really getting the crud out of that 4 pin and all the connectors actually under the right side cover and making sure they were snug. After I had sprayed the crap out of them I took the bike for a test ride. All appeared to be fine I took the bike for a brisk 20min ride to the local pool. After going for a swim I came back and the bike refused to start.

I kept giving it throttle and then full choke but nothing happened the engine turned over and I could hear the full pump engage but no ignition I also looked in the tank for fuel return and I could see some fuel being pumped back into the tank as I tried to start the bike. I tried reconnecting the 4 pin and plugging it back in nothing changed. So I attempted to push the bike home haha all 550lbs was sweating my butt off and I gave up when I passed my local bar and sat down for a bevie.

I was going to go into my onboard toolkit to check for spark at the plugs but very annoyingly I had lost my hex key to take the spark plug cover off. So I gave up and came back to the bike today. After much swearing and spraying everything in sight with deoxit while an old bloke from the Czech republic gave running commentary, I managed to take the ECU computer out and spray that connection and put it back. All of sudden the bike roared to life. I was super stoked to not have to push it all the way home!

What could be going on? I might go pull the plugs and check that all of them are sparking correctly. Could it be a faulty spark plug wire? Or maybe my ECU is bad? Or more likely something in the electrical system is intermittently causing the ignition system to fail. Doesn't seem to be only the 4pin because the pump was operating the whole time I was trying to start the bike.

Something I have also noticed is that the engine note at idle sounds quite rough and stumbly.

I have included a link to a video of my bikes stumbly idle. It looks fine of the tac but it sounds a bit weird. I don't remember it sounding this way before I had all my issues. 

https://vimeo.com/347441343

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  • New York
  • 1992 BMW K75S ABS

Offline Laitch

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #35 on: July 11, 2019, 02:07:53 AM »
Hey guys, Some more unfortunate news . . .
What's the unfortunate news? That you're not strong enough to push a moto without stopping for a bevie? :giggles It seems like you have the moto roaring to life. Is that not enough or does it roar then squeak then wheeze? Your video doesn't tell me anything is particularly wrong unless the revs are dropping but you're not closing the throttle.

What could have been going on is the FICU plug could have been making poor contact. It might not have been latched well. Pull outward on its right end and be certain it doesn't move. If it does move, its latch needs adjustment Be certain the battery connections are tight and that your negative battery cable connection on the transmission is clean and tight. If it hasn't been done already, change the feckin' fuel filter. Satisfy obsessive needs by examining the z-hose breather connecting the block to the plenum. If it were my moto, I'd replace it. It isn't costly.



Take the moto for a run. Bring along funds for another bevie.
  • Along the Ridley in Vermont.
  • 1995 K75T 72,000 miles
I wept because I had no radials until I met a man who had no splines.
http://www.motobrick.com/index.php/topic,296.msg53303.html#msg53303

Offline The Mighty Gryphon

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #36 on: July 11, 2019, 09:14:16 AM »

I kept giving it throttle and then full choke but nothing happened the engine turned over and I could hear the full pump engage but no ignition I also looked in the tank for fuel return and I could see some fuel being pumped back into the tank as I tried to start the bike.

I suspect that you flooded it and having an adult beverage gave it time to drain out the extra fuel.  Never touch the throttle when starting, and only use the choke when the engine is cold or in cold weather.   My experience with my K100RS is that some of these bikes flood very easily.
  • In my garage in Marilla, NY
  • '94 K75RT Mystic Red, '91K100RS White/Blue
Current:
'94 K75RT "Ilsa, She Wolf of the SS"
'91 K100RS "Moby Brick Too

Offline ExpatAussieBrick

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #37 on: July 11, 2019, 09:22:34 AM »
Thanks for the advice. The bike does run quite well most of the time until these sudden episodes of rough riding which seems to have progressed to sudden episodes of no start. I think I might just be imagining a rough idle note when it is actually fine due to me not entirely trusting the bike now it's left me stranded a few times.

I will try checking that Z hose and replace it. Will make sure the ECU computer is tight as well and the battery contacts. It seemed very dusty and dirty down there.

What's interesting about having flooded the engine is that yes i'm fairly sure I probably did flood it while trying to start it and make the problem worse but after leaving it for a whole day with the plugs out it still didn't start until I went and unplugged cleaned and reconnected the FICU.

Will definitely bring some cash with me for a beer on my next test ride incase it decides to act up!   
  • New York
  • 1992 BMW K75S ABS

Offline Laitch

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #38 on: July 11, 2019, 09:40:16 AM »
. . . due to me not entirely trusting the bike now it's left me stranded a few times.
With the advent of wingsuit flying, parkour along high-rise buildings, and hundred-person queues in the Death Zone of Mt. Everest, the only really cutting-edge, life-threatening personal adventures remaining are sassing the police, unprotected sex with random participants and riding an unreliable moto in traffic or wilderness.

Enjoy it!
  • Along the Ridley in Vermont.
  • 1995 K75T 72,000 miles
I wept because I had no radials until I met a man who had no splines.
http://www.motobrick.com/index.php/topic,296.msg53303.html#msg53303

Offline ExpatAussieBrick

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #39 on: July 23, 2019, 11:38:03 PM »
Hey just an update for ya on the bike

So I went ahead and got a new crankcase breather Z hose and replaced it. The old one did have a crack in it near the end of the hose.

I also took the L-Jetronic computer out fully cleaned it sprayed with deoxit and made sure it was nice and snug and clipped in.

Bike has been running with no issues this past week or so.

Think this case might be closed but will go in under the tank and tidy up the connections under there to be sure.
  • New York
  • 1992 BMW K75S ABS

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