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I have been trying to get a little more power out of my old 92 jag 440 and I did a compression test on the motor. I never did this before. I ran it around some to warm it up. Then I shut if off and tested both cylinders one at a time. One pull for each cylinder. One had 75 and the other had 85. Then I redid the test. This time I pulled 3 times for each cylinder. Then they both read 100. Is this good?
 

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The correct procedure for testing compression:

1. Pull all spark plugs out of the cylinders, reattach the plug wires, ground out the plugs (to prevent possible damage to the CDI).
2. Make sure the key is off and the kill switch is down.
3. Screw in your compression tester to your first plug hole.
4. Have someone hold the throttle wide open (or use some wire or tape or whatever to keep the throttle pinned to the bar).
5. Pull engine over 5 times.
6. Record the reading on the compression tester.
7. Release the pressure on the tester and repeat steps 3 to 6 for each cylinder.

Good readings are 125 psi or better and no more than 10% difference between the lowest cylinder reading and the highest cylinder reading.
 

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I am having the same trouble but I ran 107 MPH in 2000 feet, so I dont think the reading I got of 98 LBS in all 3 cylinders is right, by the was i've got a 1996 ZRT 600, could there be a compression problem if the sled get's those speeds.
 

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AC man perfect explaination. Only thing is I was told by the boys of ledgend performance that 8 to ten pulls are in order. I just pull to the guage stops going up. ZRT your sled sounds like its just fine.
 

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Discussion Starter #5
Wow, I did it all wrong. I was just happy to see them both at 100lbs. I will try your method when I get the tester back. My luck I will flood it.
 

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um, if the key is off and the kill switch is down, it doesn't matter if there are plugs in or not. I've never ever heard of grounding the plugs in my life. That just sounds like a pain.
 

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My take on grounding the plugs that have been pulled from the cylinders is that it's just a precautionary measure to prevent damage to the CDI if you forget the key and kill switch. If you want to skip grounding the plugs, have at it... [:)] And, pulling the plugs makes pulling the engine over for testing a whole lot easier on the arms (unless you only have a one cylinder motor, then it don't matter all that much)... [:)]
 
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