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Compression test results

Discussion in 'XJ Technical Chat' started by prince_albert3, Apr 15, 2012.

  1. prince_albert3

    prince_albert3 Member

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    I finally got around to doing a compression test. Ha, four times actually.
    I rode for about 20 minutes to get it up to normal op temps.

    Test 1
    1. 110 lbs
    2. 95 lbs
    3. 80 lbs
    4. 95 lbs
    After this test, I was confused because my bike runs great. I couldn't understand why the number were so low. "Must be a bad meter" I said to my self. I was very careful to be sure the fitting and hose were sealing well. Again, not understanding why the numbers were so low, I figured I'd run a "wet" test.

    Test 2(wet)
    1. 150 lbs
    2. 135 lbs
    3. 125 lbs
    4. 135 lbs
    For this test, I added a cap full of motor oil to each cylinder just prior to taking a reading. I did each reading a few times to be sure and record the highest results. I did find that after each wet run it gave a lower reading than the previous one, somewhere between 5-10lbs less.

    So, still contemplating my low findings, I put it all back together. As I begin to clean up my tools, it hits me. WHAM, you dummy, you ran the entire process without ever touching the throttle! Yes I did...

    Needles to say, I had to go through it all over again. The engine was cooling off but it was still a little warm. Also, keep in mind that I had just done the wet test so we'll call the 3rd results "moist", ha.

    Test 3
    1. 120
    2. 150
    3. 180
    4. 170
    Just to clarify: all plugs out, air filter out, Ignition unplugged, FULL THROTTLE. Much better this time around!

    Test 4(wet)
    1. 205
    2. 190
    3. 210
    4. 150
    Not too bad. Cylinder 4 was odd, as you can see. It must have been a misreading somehow. It had gone up the previous time but this time went down. To be fair, I may have rushed though the last run.

    Anyhow, I was much happier with the last results. Of course, they are not the most accurate do to my previous mishap. I'll run the test again after some more riding on my next day off.

    Ha, between tests 1 and 2 I found myself eying up the parts bike. I was thinking about what I would have to switch over to get the readings from it and the work involved in a motor swap.

    Anyway, I am happy with it as of now. I'll throw in some plug pics for you enjoyment!

    Cylinders in order from left to right, 1-2-3-4:

    [​IMG]

    Again, 1-2-3-4:

    [​IMG]

    1 & 2:

    [​IMG]

    3 & 4:

    [​IMG]

    4 & 1 for comparison:

    [​IMG]


    What are your thought?
     
  2. Davidkal

    Davidkal Member

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    Plugs are purty,,,,,looks good to me
     
  3. mook1al

    mook1al Member

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    Well, your results are way varied. Get/borrow another tester or two, at least one of which is verified accurate and retest.

    Plugs...1=too rich 2/3= ok, but slightly rich 4=lean...need to tune carbs.
     
  4. prince_albert3

    prince_albert3 Member

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    The results were slightly erratic. I will certainly redo the test, properly, in the next few days.

    Those were my suspicions with the plugs as well. Like I said, I took it for a little ride, pretest. By the time I had everything for the test and figured out what I was doing, I decided to let her idle for 5-6 minutes to be sure it was good for the test.

    The interesting thing is the muffler mod. I put Harley take-offs on there. I never did get them to make a tight seal where they mount on at the collector. I had to get thrifty with 2 pair of couplers and they let a little escape at the joints. I have always been aware of it and if anything thought it might cause a hair of a lean condition. Although the sound, to me, is better than stock, I have always wanted a little more. Maybe I can get away with a small bore punch for a little more...
     

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