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Compression test. First of all use a compression gauge that has been reliably used in the past. Perform the test on a motor that is Cold and Dry. Room temperature with no added oil in the cylinders. Warm motor may give false low results. Added oil in cylinders will give false high results. Remove both spark plugs and ground them to the engine block with ignition wires attached to avoid damage to the ignition system. Screw the compression gauge into the top cylinder and crank the recoil until the gauge reads as high as it will go. 3-5 quick pulls should be enough. Write down the comp reading for each pull. If the reading drops between the pulls you have a leak. If so correct the leak and repeat until you get consistent results. Repeat for bottom cylinder and write down the results.