A lot of the Evinrudes used the same powerhead for years so that wouldn't be surprising. 140psi is about what you would expect. What you don't want is a cylinder with more than 10-15% deviation, ie five cylinders read 140 and one reads 110.
When I was a kid we lived about 1300 miles from where my granddad lived and every summer we would load up the station wagon and head home for a couple of weeks around the forth. My granddad had a cabin on a lake about 10 miles out of town and had and old wooden boat that he'd let us paddle around the lake.
Fond memories, but what got me started with boating was the fact that the fish and the beach were over there and I was over here. A boat could get me from over here to over there.
You can make a pretty effective battery powered alarm system by just using a plunger switch in series with a siren wired to your battery. You might get more false positives from birds and other critters that could climb in but a motion sensor kicking on flood lights and a siren would probably be more effective.