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I have a 1996 Mercury 4 cylinder 40hp with 125 Psi across all 4 cylinders. I also have a mid 80s Mariner/ Yamaha 40hp 2 cylinder with 123 Psi both cylinders. I'm not sure what factory specs are, but maybe this would help.

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14y ago
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Q: What should the compression be on a 40 hp mercury?
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