Results 1 to 3 of 3

Thread: '87 K75S Got myself a brick! Looking for advice.

  1. #1

    Cool '87 K75S Got myself a brick! Looking for advice.

    Hey all, proud new '87 K75 owner, reporting in!

    DSC_4893.jpg

    Picked her up for a song ($500) a couple weeks ago. 46k on the clock, eng oil, filter, gearbox flush, final drive flush, brake fluid flush performed recently by BMW SF. I'm planning on diving deep and doing all future maintenance (within reason) myself. I'm real excited to build up my understanding of the whole bike top to bottom.

    When I picked the bike up it felt anemic, had a lot of afterfire on decel and the fuel economy was quite poor (20mpg!! at one point). Turns out one of the spark plug cables had come loose, after re-attaching it the bike has been a lot more well behaved and I've averaged about 46mpg over the last 200 miles. I'd like to keep riding this bike for another 150k miles so I wanna take real good care of 'er.

    Overall everything seems ok, there are a few things on my radar to check out:

    First off the bike brubles and occasionally afterfires fairly noticably when decelerating with no throttle. I hear that some K bikes just do this? I'd like to resolve the issue though if possible. I've checked the TPS contacts and they're nice and clean. Not sure where to go next?

    Second off, the idle seems... rough or maybe lumpy? It doesn't stutter so much as wander, spending 10 seconds at 1050 then 5 seconds at 900 then 7 seconds at 1k etc etc. The idle doesn't stay at the same RPM even when warm. Just now (warm engine, coming off 40 mile ride) I had the bike on the center stand upon starting idle climbed to 1200 then fell back down to 1050, in this state holding down the starter button would raise the RPM to about 1200. Blipping the throttle wide there'd be a half second or so of hesitation/chugging before the engine would revved up. Once I've taken it up past about 2k and the alternator kicks in the idle drops down to about 750, and starts sounding a bit worse. Maybe I just need to adjust the idle screw? Taking the bike off the center stand and leaning it LEFT seems to RAISE the idle RPM and leaning it RIGHT seems to LOWER it. When the bike is leaned left the throttle seems more responsive and holding the starter raises the RPM less, when leaned right the opposite is true.

    This seems like some sort of fuel delivery issue to me. I can't imagine a vacuum leak that would be affected by the tilt of the bike right? However it's an old bike and the rising RPM when hitting the starter seems like there might be a vacuum leak AND some sort of fuel delivery problem. Really unsure though, the afterfire seems to indicate a rich mixture to me, yet vacuum leak would mean it's running lean?

    I've dumped half a can of Seafoam in the tank, and I'll finish it off at next fillup to see if perhaps that helps the problem. Other than that I'm not sure where to start? Pull the gas cap and check the fuel filter and pump seems easiest. After that send the injectors to Mr. Injector? I've got a new set of spark plugs on the way, and maybe I'll grab a new air filter as well.

    Overall though, I love this bike, such a blast to ride! Looking forward to many more miles.
    Last edited by errantspark; 09-21-2018 at 03:05 AM.

  2. #2
    3 Red Bricks
    Join Date
    Jan 2007
    Location
    Pleasanton, Ca.
    Posts
    4,574
    Errant,

    Welcome to the wonderful world of Flying Bricks! You've got one of the best ones, an '87 S.

    Where in the bay area do you live? I'm over in Pleasanton.

    It actually does sound like a vacuum leak, specifically the crankcase breather hose or the 90 degree hose that connects the air filter housing to the intake plenum.

    I stock virtually every part for K75Ss and can help you learn about your bike. I own 6 of them and work on many others for people in the bay area.

    If you want to bring it by sometime, we can talk. Advise is always free.

    Looks like you bought the one that was on Craigslist that didn't have a windscreen. I've got those also.





    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

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

  3. #3
    Quote Originally Posted by 98lee View Post
    You've got one of the best ones, an '87 S.
    Sorry to disappoint! It's actually a K75C, Caribbean Blue. The fairings were swapped with ones from a black K100S, and the gas tank is the original, just repainted. Previous owner claimed he did it cause he liked the look and the bike doesn't show signs that it's been dropped. It's a clean title too but

    Quote Originally Posted by 98lee View Post
    If you want to bring it by sometime, we can talk. Advise is always free.
    I'm in Mountain View! I'd love to meet up sometime. I ordered a new set of sparkplugs that should be here sometime next week. If advice is free, how much to borrow a spark plug wrench to swap em out? One or two beers? XP

    Quote Originally Posted by 98lee View Post
    Looks like you bought the one that was on Craigslist that didn't have a windscreen.
    I actually have one, I took it off for the time being as I prefer the aesthetic of the bike without it. I hope that's not sacrilegious. I think it's a bit too tall, I'd like one that's about 1/3 of the height, just enough to keep things quiet when I put my head down.
    Last edited by errantspark; 09-21-2018 at 06:54 AM. Reason: more info

Similar Threads

  1. 1990 K75S - Rear main seal advice please!!!
    By scottishsg in forum Flying Brick K-bikes
    Replies: 17
    Last Post: 10-11-2014, 11:48 PM
  2. 1987 K75S- In a Jam on the Road: Need Advice
    By mieczkow in forum Flying Brick K-bikes
    Replies: 23
    Last Post: 10-15-2010, 05:22 PM
  3. K75s touring setup, need advice
    By Craigt in forum Flying Brick K-bikes
    Replies: 33
    Last Post: 02-27-2009, 11:06 PM
  4. K75S Advice?
    By JIMDISHMAN in forum Flying Brick K-bikes
    Replies: 4
    Last Post: 07-26-2008, 02:58 AM
  5. Advice on the low seat option: K75S
    By mieczkow in forum Flying Brick K-bikes
    Replies: 3
    Last Post: 04-15-2006, 01:17 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
  •