Results 1 to 7 of 7

Thread: 1988 K75C high idle issue

  1. #1
    Registered User rall275's Avatar
    Join Date
    Apr 2017
    Location
    Harrisburg, IL
    Posts
    59

    1988 K75C high idle issue

    Hi Guys,
    Well, I pulled off my throttle bodies and cleaned them off, replacing the 3 rubber boots and the 3 manifolds. I also changed the clamps. My problem is when I synched the fuel injectors, the #3 brass screw must be bottomed out in order for the hot idle to be around 1000. The screws for intake 1 and 2 are not all the way in when all intakes are synchronized.

    My bike idles at 1025, but if #3 would have more room to screw in I could get them all synched at a slightly lower idle.

    What could be causing #3 to require more screwing in than 1 and 2?


    The rubber caps are new, O-rings have been replaced on the needle screws. I haven't touched the TPS, but am thinking of rotating it slightly to see if that might not help. I'm also thinking about looking at the hose going to #3 an the fuel pressure regulator.


    Thanks!


  2. #2
    3 Red Bricks
    Join Date
    Jan 2007
    Location
    Pleasanton, Ca.
    Posts
    4,806
    Odds are, when you changed the manifolds, one of the hose clamps is holding the throttle linkage open. Usually it is the clamp on TB#3. That one does NOT go on in the same direction as the other two. If you try to put the clamps on simetrically, #3 will hold the butterflies open.


    Not your problem but, you should always adjust your valves BEFORE adjusting the throttlebodies.


    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

    Lee Fulton Forum Moderator
    3 Marakesh Red K75Ss
    Mine, Hers, Spare

  3. #3
    Registered User rall275's Avatar
    Join Date
    Apr 2017
    Location
    Harrisburg, IL
    Posts
    59
    Thanks Lee for your great suggestions. Here are a few photos of the orientation of the manifold clamps. This matches what they were before. Another photo shows the plenum and assembly attached after cleaning/rehab. Notable is that the lower clamp on TB 3 on the plenum had to be oriented differently from the rest.

    I'll go back in and dig around to see if there might be a throttle cable being impinged. If you have a specific area to look at please tell me.

    Thanks!

    Keith
    Attached Images Attached Images

  4. #4
    Registered User rall275's Avatar
    Join Date
    Apr 2017
    Location
    Harrisburg, IL
    Posts
    59
    Here are photos of the old manifolds as they looked with the clamp orientations. The other photo shows how the assembly sat before I removed it and rehabbed it.

    Attached Images Attached Images

  5. #5
    3 Red Bricks
    Join Date
    Jan 2007
    Location
    Pleasanton, Ca.
    Posts
    4,806
    Back off the throttle position switch so that you are SURE that it is not holding the butterflies open. If you have the #3 brass bypass screw completely closed at idle, and it is still running, air is getting into the cylinder somehow. Either the air is getting past the butterfly (being held open by TPS or one of the hose clamps) or the vacuum hose going to the fuel pressure regulator from #3 is leaking (try disconnecting the hose at the throttlebody and checking the balance without the hose teed in.

    How far open are #1 & #2 bypass screws?

    Unless you have a leak at your new manifolds, I'm beginning to think you should check the valve adjustment. How many miles ago was it last done?






    Last edited by 98lee; 07-29-2019 at 08:57 PM.
    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

    Lee Fulton Forum Moderator
    3 Marakesh Red K75Ss
    Mine, Hers, Spare

  6. #6
    Registered User rall275's Avatar
    Join Date
    Apr 2017
    Location
    Harrisburg, IL
    Posts
    59
    I haven't gotten a chance to look back into my bike, but I adjusted the valves in July of 2017. The brass screws on 1 and 2 probably are 1 to 1.5 turns out from being bottomed.

    When I get a chance, I'll check the vacuum hose, look for restrictions, and evaluate the TPS. Thanks for responding, and I'll keep you posted.

  7. #7
    Registered User rall275's Avatar
    Join Date
    Apr 2017
    Location
    Harrisburg, IL
    Posts
    59
    I think I solved the problem to my satisfaction, but I'm sure a mechanical expert would've done things differently or better.

    I tightened the clamps and relocated the one on TB3 farther back to ensure it wasn't touching the linkage. The hose to the pressure regulator seems attached. I tested after these tweaks but didn't notice any difference. I took off the T and didn't notice much other than the carbtune indicator a bit jumpier on #3.

    I did loosen the TPS and rotated it slightly and tested and was able to back out screw #3, synch the throttle bodies, and have the hot rpm at about 990. The screw is backed out from seated about 1 1/4 turns, allowing future adjustment of the idle rpm. I test rode it and the idle is about 990.

    I'll be testing the mpg since the whole catalyst of my projects (master cylinder, spiegler brake lines, front pads, radiator/fan motor/coolant stub/thermostat/coolant sensor, throttle body clean/adjust) were inspired by my somewhat low mpg. I'm not saying there's not a leak somewhere, although for the life of me I can't see how there could with as careful as I was and having replaced all the sources of leaking.



    Here's a photo of the idle while hot after my ride. I'd be ok if it were to settle at 1000 too.


    Thanks for your help and I'll ask further questions if they come up and you're willing to shoot some responses!
    Attached Images Attached Images

Similar Threads

  1. 1988 K75C 166k troubleshoot spark issue
    By pjar in forum Flying Brick K-bikes
    Replies: 4
    Last Post: 03-18-2014, 12:56 AM
  2. 1988 K75C 128 k mi. Injector question
    By pjar in forum Flying Brick K-bikes
    Replies: 4
    Last Post: 04-03-2012, 08:38 PM
  3. Back wheel locked up. 1988 K75C
    By Gil in forum Flying Brick K-bikes
    Replies: 11
    Last Post: 11-17-2010, 08:16 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •