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  • #1

    compression test

    What are people getting for compression checks on their bikes? Mine's an 82' XJ. I'm getting about 125 psi but I noticed that I'm gettting a small amount of oil back through the carbs - wondering if I have a stuck ring or something. Also, noticed upon pulling the plugs, 1,2, and 4 are black, wet and sooty, while #3 is gray and dry.... What could that mean? too much gas on 3 cylinders, not firing on 3 cylinders, too little gas on 1 cylinder?

    Tom Brant
    Tags: None
  • #2
    black

    black wet sooty,are normaly to much fuel,float level sticky needles,bla,bla bla.
    1982 XJ 1100
    going strong after 60,000 miles

    The new and not yet improved TRIXY
    now in the stable. 1982 xj11, 18,000miles

    Comment

    • #3
      Compression

      Tom, try another compression guage. These things are notorious for being close bit not accurate.
      Mine reads 158 to 160 right across. I rechecked with my neighbors gauge and got the same readings. The bike is a 78e with a 48,000 kms on it.
      Make sure that to do the test that you:
      1. Warm up the engine.
      2. Remove all spark plugs.
      3. Hold the throttle wide open while cranking.
      If you are still getting relatively low readings do a "wet" test.
      Squirt a small amount of oil into each cylinder. Spin over a few times to distribute the oil around the pistons/rings/cylinders.
      Repeat the test. If you get a big increase (12-15 lbs or more) you are due for rings. If only a small increase but still even then that is what you have. Not worth taking apart yet, but you will not make top HP.
      The fact that you are getting even readings right across is a "Good" thing.
      Ken/Sooke
      78E Ratbyk
      82 FT500 "lilRat"

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      • #4
        Tom, back in 99 the dealer did a tune up for me and reported 147 for all 4 cylinders. Last summer I replaced my cam chain and had the unfortunate opportunity to clean the head and replace the head gasket. After assembly with my gage I got 155 across all 4.
        Marty in NW PA
        Gone - 1978E - one of the first XS11 made
        Gone - 2007A FJR - the only year of Dark Red Metallic
        This IS my happy face.

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        • #5
          At 125, I'll second Ken's guess that you did not have the throttle cranked wide open when you did the test.
          Ken Talbot

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          • #6
            no throttle is correct. I can't keep the bike running but wanted to rule out a valve being stuck open or something causing it to backfire. I also only removed one plug at a time and only cranked for a few seconds.
            The readings all slowly bled down. Is that normal - the gauge may be leaking too - it is old.

            Tom B.

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            • #7
              You need to go back and re-do the test as per Ken (Ratbike's) suggestion. With using just a simple compression tester, the reading will bleed down and this is normal. The rings are not meant to hold the pressure within the cylinder for very long, especially not when things are spinning over at thousands of revs per minute.
              Ken Talbot

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              • #8
                Compression

                Tom, if you did not have the throttle open and all the plugs out then 125PSI is "GREAT" compression reading. I'm quite sure it has over 150 PSI. You have a solid engine.
                Start fixing the little things. Make the carbs work right, Get the timing right on, make sure both vacuum and centrifugal advances are working. Then start working on elbows and hand grip because it is going to "Haul Ass".
                Smile, you have a good one.
                Ken/Sooke
                78E Ratbyk
                82 FT500 "lilRat"

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