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Thread: Compression Test & the Starter Motor

  1. #1
    glen's Avatar
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    Compression Test & the Starter Motor

    Hey all,
    I tried to run an engine compression test on my '97 ST1100 as per the instructions in the Clymer service manual. According to the book, I should be able to crank the engine with the starter motor while the engine stop switch is OFF. However, my starter motor does nothing without the engine stop switch engaged. Any ideas what I'm doing wrong, here?

  2. #2
    Brant's Avatar
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    Re: Compression Test & the Starter Motor

    The STOP/Run switch electricly completes the running circuit, and likely completes the starting circuit also.
    1992 ST1100
    1981 Yamaha XS Venturer 1100

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    SMSW's Avatar
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    Re: Compression Test & the Starter Motor

    You will have to do the test with the STOP switch in the run position. Make sure all plug wires are away from your hands - the shock can be surprising.

  4. #4
    Bush's Avatar
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    Re: Compression Test & the Starter Motor

    All those plug wires should also be grounded to the engine while turning the engine over.

  5. #5
    240Robert ST Gui's Avatar
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    Re: Compression Test & the Starter Motor

    Quote Originally Posted by glen View Post
    According to the book, I should be able to crank the engine with the starter motor while the engine stop switch is OFF. However, my starter motor does nothing without the engine stop switch engaged. Any ideas what I'm doing wrong, here?
    I'm guessing that's an error in the Clymer manual. This was possible in some older Hondas I had.

    Honda changed that maybe so that some people wouldn't kill the battery trying to start the bike with the switch inadvertently left in the Off position. I don't know.

    I do know I feel a little less stupid when hitting the starter and nothing happens because I made the same mistake. Harder for the casual observer to note my rookie mistake.
    Don't tell me what I know. Tell me what I don't know.

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  6. #6
    Oldbikefixr's Avatar
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    Re: Compression Test & the Starter Motor

    I have a 1991 1100. It WILL crank with the kill switch engaged. On the center stand, side stand either up or down...still cranks. With the bike on the side stand, it will not crank regardless of the position of the kill switch.

  7. #7
    Bush's Avatar
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    Re: Compression Test & the Starter Motor

    Not sure what year it changed - my '95 would not crank with the switch off, but early models did allow this. Think I remember reading about it in the old ST1100 Newsletters.

  8. #8
    Site Supporter Don B's Avatar
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    Re: Compression Test & the Starter Motor

    Quote Originally Posted by Bush View Post
    All those plug wires should also be grounded to the engine while turning the engine over.
    How about simply unplugging the coil primary wires and insuring they won't touch anything that can ground them?

    The Older I Get ... The Better I Was

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  9. #9
    Oldbikefixr's Avatar
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    Re: Compression Test & the Starter Motor

    Quote Originally Posted by Don B View Post
    How about simply unplugging the coil primary wires and insuring they won't touch anything that can ground them?
    That's what I do whenever I perform a compression test. Makes sense to check the spark at the same time.

  10. #10
    Bush's Avatar
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    Re: Compression Test & the Starter Motor

    Quote Originally Posted by Don B View Post
    How about simply unplugging the coil primary wires and insuring they won't touch anything that can ground them?
    Sounds like more work to me. Just leave the plugs in the leads and ground the plugs on the engine.

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