Author Topic: 85 K100RT possible vaccum or fuel issue?  (Read 627 times)

Offline gallowsbound

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85 K100RT possible vaccum or fuel issue?
« on: May 14, 2018, 03:03:52 PM »
1985 K100 RT


This was a project i turned into a naked bike.
Anyway, i believed the bike to be in top shape after completion but after a 12 or 15 mile ride in 100 F temps, i think maybe not.


Its a simple symptom. Once the bike was up to temp the throttle would bog and nearly die. It would lurch and cough. Then after every episode I would stop, turn the bike off..wait 30 seconds or so, fire it up and it was good for another few miles then repeat the same procedure.


The mods to the intake and vacuum were small but may have my verdict in their simplicity.
I did an exposed MAF sensor with a filter as has been done. Additionally, I deleted the crankcase breather hose and replaced it with a filter and plugged the outlet on the plenum itself.


Other than all that the bike was mainly hacked up cosmetically with no other major mechanical changes.


I just think it is bizarre behavior for the problem to arise then once i stop the bike, shut it down and start again it is fine for a bit then starts again.
Thoughts? Concerns?


85 RT KCMO
  • kansas city
  • 1985 BMW K100RT

Offline Martin

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Re: 85 K100RT possible vaccum or fuel issue?
« Reply #1 on: May 14, 2018, 03:38:14 PM »
Check the return line from the FPR to the tank. make sure it is not kinking when you slide the tank back into position.
Regards Martin.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline gallowsbound

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Re: 85 K100RT possible vaccum or fuel issue?
« Reply #2 on: May 14, 2018, 03:42:55 PM »
Will do a check when I get home and report back.


Thanks
  • kansas city
  • 1985 BMW K100RT

Offline gallowsbound

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Re: 85 K100RT possible vaccum or fuel issue?
« Reply #3 on: May 15, 2018, 03:52:03 PM »
Nope. not kinked or anything. I blew out and cleared the line. Nothing there either.
  • kansas city
  • 1985 BMW K100RT

Offline Martin

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Re: 85 K100RT possible vaccum or fuel issue?
« Reply #4 on: May 15, 2018, 04:01:30 PM »
Check the fuel pressure and when was the fuel filter last changed?
Regards Martin.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Online Laitch

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Re: 85 K100RT possible vaccum or fuel issue?
« Reply #5 on: May 15, 2018, 04:12:28 PM »
Its a simple symptom. Once the bike was up to temp the throttle would bog and nearly die. It would lurch and cough. Then after every episode I would stop, turn the bike off..wait 30 seconds or so, fire it up and it was good for another few miles then repeat the same procedure.
Try this test. http://www.motobrick.com/index.php/topic,3308.msg20124.html#msg20124
  • Along the Ridley in Vermont.
  • 1995 K75T 68,000 miles
I wept because I had no radials until I met a man who had no splines.

Offline gallowsbound

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Re: 85 K100RT possible vaccum or fuel issue?
« Reply #6 on: May 15, 2018, 04:13:39 PM »
Fuel pressure is within spec. As far as the fuel filter...who knows when it was changed. Is there an available aftermarket replacement or is it a dealer spec part only?
  • kansas city
  • 1985 BMW K100RT

Offline gallowsbound

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Re: 85 K100RT possible vaccum or fuel issue?
« Reply #7 on: May 15, 2018, 04:19:05 PM »
Try this test. http://www.motobrick.com/index.php/topic,3308.msg20124.html#msg20124


I will try this test after work today as well as change a fuel filter...since i have no idea when that was done.
  • kansas city
  • 1985 BMW K100RT

Offline Martin

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Re: 85 K100RT possible vaccum or fuel issue?
« Reply #8 on: May 15, 2018, 04:47:44 PM »
You might want to clean and check the 4 pin connector to the fuel pump. A mates bike had similar symptoms.
Regards Martin.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline johnny

  • TrailBrakingThrottleWhacker
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  • Whacking...n...Chopping Sliding...n...High Siding
Re: 85 K100RT possible vaccum or fuel issue?
« Reply #9 on: May 15, 2018, 04:57:14 PM »
greetings...

1) where are the photos of this naked moto...
2) does it do it when you ride it with the gas cap open...
3) does it do it after you do this...

http://www.motobrick.com/index.php/topic,11033.0.html

please advise..

j o
  • i parks my 96 eleven hundert rs motobrick in dodge county cheezconsin...
:usa#1

Offline gallowsbound

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Re: 85 K100RT possible vaccum or fuel issue?
« Reply #10 on: May 16, 2018, 12:13:04 PM »
greetings...

1) where are the photos of this naked moto...
2) does it do it when you ride it with the gas cap open...
3) does it do it after you do this...

http://www.motobrick.com/index.php/topic,11033.0.html

please advise..

j o


I have photos but i keep getting errors that they wont attach??? Files too large? Suggestions?


It seemed to be a faulty fuel filter. It was installed incorrectly and was also clogged. Thanks previous owner!!
Anyway, it was raining yesterday in KC but today is sunny and warm. I will ride the piss out of it after work and see what happens with a fresh filter and clear FPR lines.



  • kansas city
  • 1985 BMW K100RT

Offline gallowsbound

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Re: 85 K100RT possible vaccum or fuel issue?
« Reply #11 on: May 16, 2018, 12:23:07 PM »
Still some aesthetic work. Some aluminum perforated panels for side covers and wheel upgrades.


Some mech work will include my new exhaust i am fabbing up, rearsets, and some other misc items.
  • kansas city
  • 1985 BMW K100RT

Offline johnny

  • TrailBrakingThrottleWhacker
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  • Whacking...n...Chopping Sliding...n...High Siding
Re: 85 K100RT possible vaccum or fuel issue?
« Reply #12 on: May 16, 2018, 01:33:43 PM »
greetings...

thanks for sharing... needs a supercharger...

j o
  • i parks my 96 eleven hundert rs motobrick in dodge county cheezconsin...
:usa#1

Offline gallowsbound

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  • Posts: 13
Re: 85 K100RT possible vaccum or fuel issue?
« Reply #13 on: May 16, 2018, 01:54:11 PM »
greetings...

thanks for sharing... needs a supercharger...

j o


I am still shocked at how damn cool the block on these things are. I always despised BMW design, mainly airheads because it was all i had ever really seen. I had always built choppers--American, Jap or British. Then last summer i was doing this XS650 bobber and this was just sitting at the shop for sale. Most of the fairings gone, half naked, not running and left for dead. Then i started looking into K bike mods and was so stoked on what I saw. SO i bought this thing 3 months ago, got it running, did my mods and here we are.


Definitely not finished with it but its my bike for the season while I start a new chop project.


Super fun bike and all I have invested is 800 bucks lol bike and everything.
  • kansas city
  • 1985 BMW K100RT

Offline The Mighty Gryphon

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Re: 85 K100RT possible vaccum or fuel issue?
« Reply #14 on: May 17, 2018, 08:52:39 AM »
Is that a Honda Super 90 in the background?  I had my very first moto crash on a red one around 1966.
  • In my garage in Marilla, NY
  • '94 K75RT Mystic Red, '92K100RS White, '94 K75S Dakar Yellow
Current:
'94 K75RT "Ilsa, She Wolf of the SS"
'94 K75S "Cheetos"
'91 K100RS "Moby Brick Too

Offline gallowsbound

  • Motobrick Curious
  • Posts: 13
Re: 85 K100RT possible vaccum or fuel issue?
« Reply #15 on: May 17, 2018, 09:18:24 AM »
Yup! That is an S90. There are few of those floating around the shop. We have a trail 90 also...I just need to make it stop smoking like a two stroke :hehehe
  • kansas city
  • 1985 BMW K100RT

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