Author Topic: 1987 K75 poor running  (Read 8972 times)

Offline stokester

  • ^ SuperNatural Motobricker
  • Posts: 802
Re: 1987 K75 poor running
« Reply #25 on: October 31, 2019, 12:30:09 AM »
The way I understand this problem is that your motorcycle starts and idles OK but bogs down when opening the throttle.  Is this correct?
I start with basics, it sounds like too much or not enough fuel or a weak spark which may be caused by multiple problems.  Knowing the basic problem will help guide the diagnosis.

Although the plugs are new, what do they look like after it bogs down?
  • Yorktown Virginia
  • '94 K75S Dakar Yellow - '93 K75S Seiden Blau - '91 R100RT Bermuda Blue- '78 R100S Smoke Red

Offline volador

  • ^ Quintessential Motobricker
  • Posts: 1165
  • NEEDS MORE CHROME
Re: 1987 K75 poor running
« Reply #26 on: October 31, 2019, 02:23:39 AM »
Is the petrol tank venting properly? During moto idling if you open the petrol filler cap is there a pronounced "Swoosh" of a lack of air in the tank?
If so may have a blocked tank vent http://www.motobrick.com/index.php/topic,12374.msg109410.html#msg109410

There is also a grounding point on left side under the tank

"The PO had also replaced the fuel injectors."
Verified fuel injectors are working properly?

Verified ignition timing? Hall Effect Sensor?
  • NYC NY
  • 1991 K100RS 1993 K75S ABS
5 BOROUGHS SISYPHEAN SOCIETY  MAINTAINING THE OBSESSION

Offline The Mighty Gryphon

  • Administrator
  • ^ Quintessential Motobricker
  • Posts: 6617
Re: 1987 K75 poor running
« Reply #27 on: October 31, 2019, 08:05:15 AM »
Do the spark plugs have terminal nuts???   NGK plugs don't come with them.  That's why I asked for photos,  to confirm that you have them.  The bike won't run for shiite without them if you still have the original wires.
  • In my garage in Marilla, NY
  • '91K100RS White/Blue
Current:
'91 K100RS16V "Moby Brick Too"

Past:
'94 K75RT "Ilsa, She Wolf of the SS"
'92 K100RS16V "Moby Brick" (RIP, deceased in a vehicular assault)
'94 K75S Special Edition Dakar Yellow "Cheetos"
'89 K100RS Special Edition "Special Ed"

Offline volador

  • ^ Quintessential Motobricker
  • Posts: 1165
  • NEEDS MORE CHROME
Re: 1987 K75 poor running
« Reply #28 on: October 31, 2019, 11:50:21 AM »
Do the spark plugs have terminal nuts???   NGK plugs don't come with them.  That's why I asked for photos,  to confirm that you have them.  The bike won't run for shiite without them if you still have the original wires.

You dab any green threadlock on those sparkplug caps?
Ever have one loosen up on the road?
Any change in moto performance?
  • NYC NY
  • 1991 K100RS 1993 K75S ABS
5 BOROUGHS SISYPHEAN SOCIETY  MAINTAINING THE OBSESSION

Offline kenrams

  • Curious
  • Posts: 9
Re: 1987 K75 poor running
« Reply #29 on: November 02, 2019, 05:12:40 PM »
Solved!

Thank you, everyone, for your comments and help. It was a great learning exercise for me to go through the bike in what I thought was a logical step by step procedure. I hate it when threads just end with no solution, so I will eat a bit of humble pie and reveal the actual problem. https://www.motobrick.com/Smileys/default/donkey.gif

I pulled the spark plugs and checked for a nice big spark and sure enough, I had that on all three. They were all sooty and a little bit wet - not good but I moved on to the next thing. I should have dug a bit deeper when I had them out the first time. Like a few of you suggested I went back to the start this morning after I fitted the radiator back on and that's when I found it - HT leads for 1 & 3 were swapped !! Not sure when that happened but maybe I got it that way or I did it during my investigation. Just took it out for a short spin and it feels great.

Thanks a lot everyone
  • Asheville, NC, USA
  • 1985 K100, 1990 K75, 1982 R100

Offline caveman

  • ^ Proficient Motobricker
  • Posts: 196
Re: 1987 K75 poor running
« Reply #30 on: November 03, 2019, 06:50:34 AM »
Glad you found the problem and thanks for giving it up, I have done things like that too.
  • Kennerdell, PA.
  • 87 K100RT, 88 K100LT

Offline The Mighty Gryphon

  • Administrator
  • ^ Quintessential Motobricker
  • Posts: 6617
Re: 1987 K75 poor running
« Reply #31 on: November 03, 2019, 12:51:38 PM »
Thanks for the update!  That foldback on the #3 wire(#4 on the k100) has fooled a lot of folks on their first spark plug change.
  • In my garage in Marilla, NY
  • '91K100RS White/Blue
Current:
'91 K100RS16V "Moby Brick Too"

Past:
'94 K75RT "Ilsa, She Wolf of the SS"
'92 K100RS16V "Moby Brick" (RIP, deceased in a vehicular assault)
'94 K75S Special Edition Dakar Yellow "Cheetos"
'89 K100RS Special Edition "Special Ed"

Offline stokester

  • ^ SuperNatural Motobricker
  • Posts: 802
Re: 1987 K75 poor running
« Reply #32 on: November 03, 2019, 01:04:04 PM »
Thanks for running this thread to conclusion.
  • Yorktown Virginia
  • '94 K75S Dakar Yellow - '93 K75S Seiden Blau - '91 R100RT Bermuda Blue- '78 R100S Smoke Red

Offline beemuker

  • ^ Quintessential Motobricker
  • Posts: 1110
Re: 1987 K75 poor running
« Reply #33 on: November 03, 2019, 02:24:24 PM »
Thanks for running this thread to conclusion.
Good for you. Some threads are never concluded. My flashers are acting up again. good grief! I'm just using hand signals till it gets too cold to ride, then I'll revisit the whack.
  • Panama City, FL
  • '00 R1100RT,’92 K75 RT,past tense:'83 R80ST, '93 K1100LT,,94 R1100RS K75s, Honda NC700, Suzuki Bandit 1200, bmw R75/5 Honda 750

Offline daveson

  • ^ Quintessential Motobricker
  • Posts: 1027
Re: 1987 K75 poor running
« Reply #34 on: November 03, 2019, 03:06:43 PM »
Another thank you for including the solution.
  • Victoria, Australia
  • Current;'85 K100RT~100,000km; four other bricks. Past; 1500 Vulcan, V Star 650, KLX 250(dirt bike) TT250(dirt bike)

Offline volador

  • ^ Quintessential Motobricker
  • Posts: 1165
  • NEEDS MORE CHROME
Re: 1987 K75 poor running
« Reply #35 on: November 05, 2019, 10:06:09 AM »
Foldback wire #3 should be looped as such to prevent kinking

  • NYC NY
  • 1991 K100RS 1993 K75S ABS
5 BOROUGHS SISYPHEAN SOCIETY  MAINTAINING THE OBSESSION

Tags: