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Thread: K75S Performance Tuning

  1. #1
    tz750s
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    Cool K75S Performance Tuning

    Hey, new to the club and forum. I am looking to coax some more ponies out of my 1987 K75S. Are there any tried and true mods, maybe some old threads I can review? I cant seem to find much info for this topic. Thanks in advance for your time and replies.

  2. #2
    Rider
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    Orlando Florida near UCF
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    There is a maintanance video that has worked miracles for me. I am not the most mechanically oriented person, but this video makes me perform like a pro.

    Follow this thread.

    http://www.bmwmoa.org/forum/showthread.php?t=20070

    Where are you? Chances are, there will be a tech day in your area soon.

  3. #3
    tz750s
    Guest
    I am in Portland, Or. I was not really looking for maintanence, but performance mods. As long as these have been out and about ,and with the following they have, I am hoping something has been figured out to wake them up a bit. I realize this is not a sportbike, but I can't help but think there are a few more horsies in there waiting to get out.

  4. #4
    3 Red Bricks
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    The first place to start is to make sure all the stock specs. are optimised.

    It's amazing how much difference a proper valve adjustment makes (tight side of spec. on the intakes, loose end of spec. on the exhaust). Proper throttle body sync and balance will make a K75 run as smooth as an electric motor.

    After that, checking the air/fuel ratio at cruise rpms with an exhaust analizer will tell you if you have one of the air flow sensors that was set extremely lean. They can be disassembled and recalibrated.

    Then you can start bumping the timing a couple of degrees.

    I have an '87 that was built in the first week of U.S. spec K75S production (May '86 Ser.#81) with 94,000 miles on it and with the large Rev-Pac Tour bag full of camping gear and the larger 3rd generation integral cases was still accelerating hard in 5th gear at an indicated 120mph this last weekend. It had never run like that until after I did the first valve adjustment that it had had since I bought it 11,000 miles ago.

    I have yet to richen the cruise mixture or bump the timing. But that is next on the agenda as soon as the priority list gets back to working on MY bike.

    Trying to do something to make any vehicle faster without optimising the stock specs and eliminating any basic tuneup problems is like putting track shoes on a fatman. It might look fast but it ignores the basic problem and the source for the most gain. Whoops! I'm fat! I could probably make my bike a lot faster by loosing 30 lbs!


    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

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

  5. #5
    Registered User breyfogle's Avatar
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    Quote Originally Posted by tz750s View Post
    .... I am looking to coax some more ponies out of my 1987 K75S. Are there any tried and true mods, maybe some old threads I can review? I cant seem to find much info for this topic.
    You will not find much info on K75 performance mods. The few I have read about usually end up with more problems than gains. The 2 valve head rather limits how much extra HP can be extracted.

    IMO, the K75 is the wrong bike to hop-up, cheaper to buy a CBR/GSXR/FZR/etc....
    '89 K75S Original Owner
    '94 (Beta) R11RS, ( RIP 12-5-2010 courtesy of blind left turning cage driver ) ....

  6. #6
    tz750s
    Guest
    [I]"Trying to do something to make any vehicle faster without optimising the stock specs and eliminating any basic tuneup problems is like putting track shoes on a fatman. It might look fast but it ignores the basic problem and the source for the most gain. 98lee"

    Great advice, I have done the basics including syncing the carbs. I will check the valves though. The bike runs very smooth, like a swiss watch.

    "IMO, the K75 is the wrong bike to hop-up, cheaper to buy a CBR/GSXR/FZR/etc....
    breyfogle"


    I understand what you are saying, I am not trying to make a busa killer. I was just hoping to open her up a bit and let her get some air. I have other bikes for other purposes. I knew I was trying to walk off the beaten path a bit, but I just figured someone has to know something as long as these bikes have been out.

  7. #7
    A bozo on the bus deilenberger's Avatar
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    The K75S I owned had all the go-fast tricks done to it. Polished/ported head, trick air filter (POS K&S). In back to back dyno tests to a bone stock K75RT - they were identical. I put the K75S as back to stock as I could (couldn't unpolish the head) - and still no power difference. Aftermarket exhausts were dyno'd on several bikes vs stock - and the aftermarket ALWAYS lost power compared to the stock exhaust.

    The only way to get a bit more power from the K75 engine is advancing the ignition about 3-4 degrees. This is covered in detail in the IBMWR K-tech pages.

    If you want to see the dyno run results - they're on my personal website - dig around a bit on the K75S page, there should be links there..

    http://www.eilenberger.net

    Shortcut to the dyno curves: http://www.eilenberger.net/K75S/dyno.htm

    If you want more power - you really want a different bike. The power isn't laying on the table waiting for someone to walk along and pick up cheaply.

    Oh - one way to guarantee more power - but probably less reliability - there was a turbo kit made for the K75 engine for a brief period. Pricey - and made the bike even hotter than it normally is due to all the extra exhaust plumbing... but it did make more power.
    Don Eilenberger http://www.eilenberger.net
    Spring Lk Heights NJ NJ Shore BMW Riders New Sweden BMW Riders
    '07 R1200R (current ride) and some bimmers.. and a Porsche

  8. #8
    tz750s
    Guest
    Thanks deilenberger,
    Your website info on the K75S was great, I learned alot. Thanks for taking the time to document all of that. I will just enjoy the bike for what it is. Thank you all for the help.

  9. #9
    Registered User 119240's Avatar
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    I looked into this as well - I talked to Tommy up here in Ma. ( Dunbar Cycles )
    He races bike around the US - he's the type of person you need to talk to. " Sure, I can sell you this and that for your K75S to a tune of 5K +, but it's only gonna empty your wallet in doing so". He said "A STONE IS A STONE" get a new bike !!
    So I stayed with what I had for three years - recently totaled me K75S and are looking for a larger, lighter bike, new bike. Good luck
    '91 K75S, '06 K1200S
    BMWMOA #119240
    YB # 1463
    NRA #154764753

  10. #10
    Registered User
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    One "hop-up" that might give you an edge would be in the realm of suspension. The front suspension on the S model is pretty good, but that rear shock can stand an upgrade. I ran a Works Performance on mine, but I suspect that others (Ohlins, Wilbers, WP, etc) are probably available as well.
    Ride Safe, Ride Lots

  11. #11
    A bozo on the bus deilenberger's Avatar
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    Quote Originally Posted by 119240 View Post
    So I stayed with what I had for three years - recently totaled me K75S and are looking for a larger, lighter bike, new bike. Good luck
    Hmmmmm..... Max BMW has some good deals on R1200R's.. and it's larger (by a bit), much lighter (by a quite a bit) and new.. also has about double the rear-wheel HP, and modern suspension. IMHO - it's the best thing BMW is peddling these days.. but I'm probably prejudiced..
    Don Eilenberger http://www.eilenberger.net
    Spring Lk Heights NJ NJ Shore BMW Riders New Sweden BMW Riders
    '07 R1200R (current ride) and some bimmers.. and a Porsche

  12. #12
    crgrbrts
    Guest

    "...looking for a new (lighter) bike."

    I've been riding an R1200ST service loaner from Bob's BMW for a couple of days and had ridden the same bike a few months ago.

    I love it!

    At first I was put off by the angular front end styling, but I've grown to find it very pleasing -- and my wife, who has a superb design sense, thinks it's absolutely beautiful. The performance is first class -- quick, nimble, responsive. The built-in low seat option gives me flat footed assurance, which is a first for me on a Beemer. It's noticeably lighter than my K75S and thus easier to manage in parking lots and at stop lights. Its engine is smooth (though not as silky as my K75S, of course) and has very long legs on the highway. Cruising along at the functional DC-area highway speed limit of 80 feels almost leisurely and getting up to that speed requires a very few seconds and no gritting of teeth at all.

    Unfortunately for me, there's no way I can afford this $15K beauty right now -- but maybe you can. If so, I'd highly recommend a test ride.

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