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Thread: K100 Throttle Bodies

  1. #1
    Registered User
    Join Date
    Jun 2011
    Fort Myers, Florida

    K100 Throttle Bodies

    I got a used 1989 K100rs. It had a rough spot at 2500 RPM and an increased idle ( about 1100 rpm). I discovered a vacuum leak by spraying carb cleaner around the intake manifolds. I replaced both the manifolds and the bushings from the air box to the throttle bodies. It really smoothed the bike out but the idle speed then increased to about 1500 RPM. Checked for leaks again but found none. I could not get the vacuum settings right. Numbers 1, 2 and 3 bypass screws needed to be turned way out while number 4 was almost seated/closed.
    I read the excellent 2008 thread titled "K100 the throttle body adjustment?" which lead me to question my TB settings. I removed the Throttle Bodies again to check. While doing an examination I found that with the throttle fully closed, I can see daylight around the butterfly in number 4 throttle body but not on 1, 2 and 3.
    There are three adjusting screw for the TB factory adjustments I see no way to adjust number 4. This leads me to believe that someone has tweaked these screws. The blue lacer is still on the screws but I suspect they have been moved to adjust for the vacuum leak. I did not move them and I have a Clymer manual that clearly states not to touch these screws.
    My questions:
    Should number 4 butterfly be closed as well or is there any reason that it is "special?"
    If the above mentioned procedure, from the 2008 thread has to be done, are there any other tips or 'gotchas that one needs to know?
    Am I better off purchasing a used throttle body on Ebay or Beemerboneyard?
    Any advise would be appreciated.
    Last edited by whm1226; 07-17-2011 at 01:10 PM. Reason: Clarification
    Bill M
    Fort Myers Florida
    1975 R75/5, 1978 R80/7
    1989 K100rs, 2004 K1200GT, 2010 R1200RT

  2. #2

    k100 throttle bodys

    good morning bill;

    to begin i am no super genius or anything . but after taking my 85 k100 to the dealer
    it came back with the #2 cylinder butterfly plate holding everything open so idle was around 1500. long story short it took me a whole season of riding to figure it out. once I removed the throttle body itself I could see #2 was open at least 1/16 of an inch by eyeball. this is by memory but . Take your t.b. in hand analize it, draw pictures ,understand how it operates. I beleive it is #3 that has no adj. BEcause that is where the cable hooks up. adjust the small screw between 3 and 4 untill it look like the plate is the same as the others. to further the accuracy take 4 small pieces of piano wire or small drill bits and let the plates hold them tight in the t.b. bore hold at a slight angle rotate cable wheel all 4 should drop at the same time. it is going to be a WHOLE lot closer than you have. syncing can easily be done with a 2 port tool if everything else is in spec. hope this helps if you need more info send me a p.m. as the grammer police on this sight piss me off .but we CAN get your bike back on the road

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