Re: 1990 Evinrude 40 HP Compression
There is no spec. That is why you couldn't find one.
The psi you read depends on too many variables: Guage, temperature, technique and other factors that affect the reading.
For that reason, the spec is that the cylinders read within 10-15% of each other, regardless of the psi.
There is a hole in this standard response for a 2 cylinder engine: a blown head gasket between the cylinders. That would cause near equal readings, but very low. . . below about 30psi.
I generally accept readings of above 75-80 psi as satisfactory, provided that the cylinders are within the 10-15% margin.
