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Thread: 1983 gs450 cranks & won't start

  1. #1
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    Unhappy 1983 gs450 cranks & won't start

    Rebuilt a 1983 GS450. Was my daily driver last year until I put it away in December.

    Took the winter/spring to go over the bike and rebuild, refurbish, and replace anything and everything that needed it.

    Bike is back together, engine cranks but doesn't start.

    Got spark
    Got fuel (premium too!)
    Got compression

    ... I don't know why she won't fire up.

    https://www.dropbox.com/s/ulr4wc233b...31503.mp4?dl=0

  2. #2
    cowboyup3371's Avatar
    cowboyup3371 is offline Forum LongTimer Past Site Supporter
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    What is the battery voltage before and during the time you are trying to start it?

    Cowboy Up or Quit. - Run Free Lou and Rest in Peace

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  3. #3
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    Double check that plug wires are on correct plugs.
    Sounds like my bike when I didn’t use petcock prime long enough….make sure “choke” is fully “on” and don’t use any throttle during cranking.
    1981 gs650L

    "We are all born ignorant, but you have to work hard to stay stupid" Ben Franklin

  4. #4
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    Quote Originally Posted by cowboyup3371 View Post
    What is the battery voltage before and during the time you are trying to start it?
    13.1v - 12.9v Battery is still strong

  5. #5
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    Quote Originally Posted by tom203 View Post
    Double check that plug wires are on correct plugs.
    Sounds like my bike when I didn’t use petcock prime long enough….make sure “choke” is fully “on” and don’t use any throttle during cranking.
    All good points, I read elsewhere on this site. Coils are wired properly, petcock set to PRI, and choke is full send.

  6. #6
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    First things I checked were

    - grounds
    - battery
    - starter solenoid
    - starter
    - coils
    - spark plugs
    - fuel line/carburetors
    - compression

    Going to test compression again as all the above are solid

  7. #7
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    https://flic.kr/p/2mAXtZz Cylinder 1 - Dry compression test

    https://flic.kr/p/2mANCXj Cylinder 2 - Dry compression test

    https://flic.kr/p/2mAWgME Cylinder 1 - Wet compression test

    https://flic.kr/p/2mASUcd Cylinder 2 - Wet compression test

    Looks like I now need new piston rings...

  8. #8
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    Quote Originally Posted by StarcrossedMoto View Post

    Looks like I now need new piston rings...
    Just an opinion from a non-mechanic, but I'd say that at 115 on both cylinders, you're good. Spec probably says that 120 is the low limit, but I've also read that 100-105 would be the absolute low service limit. Maybe that's different on the twins, I don't know. New rings certainly won't hurt, I just don't know that this is causing the bike to not even cough when you try to start it.

  9. #9
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    105psi should run fine, and if the ring packs are sticking slightly, they'll usually free up with use.
    Only worry about new rings if they dip below 100.
    Heck, I'd only bother once the damn thing simply wouldn't start and a test revealed 70psi or so.
    ---- Dave
    79 GS850N - Might be a trike soon.
    80 GS850T Single HIF38 S.U. SH775, Tow bar, Pantera II. Gnarly workhorse & daily driver.
    79 XS650SE - Pragmatic Ratter - goes better than a manky old twin should.
    92 XJ900F - Fairly Stock, for now.

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  10. #10
    Gorminrider is offline Forum Sage Past Site Supporter
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    1: How did the rings wear out when you weren't riding it?
    2: did you have the throttle wide open when testing compression?

    that is to say, the bike you stopped riding last year is the same bike this year, engine wise. So Something Else has changed: aka gummed, rotted, been "refurbished" or "replaced"
    Last edited by Gorminrider; 10-16-2021 at 10:23 AM.

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