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Compression test results- next step?

Discussion in 'XJ Technical Chat' started by oneuglybike, Aug 4, 2009.

  1. oneuglybike

    oneuglybike Member

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    Hey guys,

    Sorry to ask a question that has undoubtedly been asked a million times. I completed my compression test and my results were much better than i expected:

    1 135
    2 130
    3 130
    4 140

    Does that seem a little low? i didnt try adding oil into the cylinder as it got dark. Those questions aside, i assumed i would have big problems with cylinder 3 because it pretty much NEVER fires.

    I guess a complete carb teardown is my next step, right?

    to give you the basics, my bike does not currently run (although it did very briefly tonight on starter fluid) and when it did, it ran minus cylinder 3 and smelled like a 1970-something pickup truck i had to follow home the other day. Burnt oil and slow engine death.

    thanks for your expertise guys,

    Mike
     
  2. wizard

    wizard Active Member

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    Your numbers are fairly even across the 4, which is good, did you test with the air filter out & wide open throttle?
    If you test again using a tablespoon of oil down each plug hole, if the readings go up it means the rings are poor & if the readings stay the same the problem is with the valves.
     
  3. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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    Actual numbers aren't as important as the comparisons. You're in good shape; I'll bet if you used a different gauge you'd get different but equally comparable readings.

    What bike, how many miles, and what issue besides the misfire are you experiencing?
     
  4. oneuglybike

    oneuglybike Member

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    thanks guys; its an 81 650 Max with about 35K miles.

    I did my test with the filter removed and the throttle wide open. Other than the misfire, it generally smoked and stank. The bike often didnt start although it would turn over. because the headlight would dim during these attempts i assumed that they were battery related. i replaced the battery a few days ago.
     

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