Equal across all cyclinders is the most important thing, within 10% is acceptable. I never was able to find actual specs for my Johnson, but all 6 range from 114 to 118 lbs so I think she's still in good shape.
I have a 65 and a 67 Merc 500. My 67 has 105-110 across all four. My 65 averages around 100 on all four. Still plenty of power. These compression readings are at 6500 feet. You flatlanders will have higher readings.
Different people, using different guages, under different conditions and using different technique may get as much as a 50psi difference on the same engine.
Don't worry about psi. Look for all cylinders to be within a 10% range.
I have a 65 and a 67 Merc 500. My 67 has 105-110 across all four. My 65 averages around 100 on all four. Still plenty of power. These compression readings are at 6500 feet. You flatlanders will have higher readings.
