I’ve run a 5hp single cylinder 4-stroke engine that was in the low 60s for psi if I remember correctly (though the compression tester I used seemed worn – it had a bent needle). That engine ran wonderfully and was a first pull engine once primed, so I think 50 psi is enough to run.
Some people have found a little lubricant in the cylinder will increase the reading, if you haven’t tried that yet.
