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Thread: 1985 K100RT - What is this?

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  1. #1
    Fred Trimble
    Join Date
    Mar 2009
    Location
    Royal Oak, MI
    Posts
    65

    1985 K100RT - What is this?

    Is it the vaccum switch? It appears to connect to the front cylinder manifold. If it is the vaccum switch, what's it's connection to starting? Thanks.
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    Fred Trimble
    1985 K100RT
    2009 R1200RT

  2. #2
    Registered User
    Join Date
    Sep 2007
    Posts
    1,248
    The vaccum switch is connected to the ignition control unit. When the control unit gets a steady high vaccum signal, which would indicate cruising at a moderate speed, it advanced the ignition timing by 12 degrees. This gave these bikes impresive gas mileage, but they tended to accelerate slightly when the timing advanced. Service school instructors suggested they be disconnected, and most of them have been by now. There is no effect on starting.

  3. #3
    Fred Trimble
    Join Date
    Mar 2009
    Location
    Royal Oak, MI
    Posts
    65
    Thanks, LB. The hose at the manifold is badly cracked. If I just cap the vaccum port and leave the switch connected electrically, will this affect drivability?
    Fred Trimble
    1985 K100RT
    2009 R1200RT

  4. #4
    Registered User
    Join Date
    Sep 2007
    Posts
    1,248
    I doubt you'll notice a difference-except that you've sealed a leak!

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