I have both an Evinrude and Johnson version of that motor that ran and idled well. They need about 120 psi to run well as I recall.

In my book the best single they ever built was the 1948 through 1951 Sportsman., , , 😎

Well…It’s kind of an all on nothing deal for these little engines….Either they idle pretty darn nice, or they won’t idle at all regardless of the normal carb/ignition repairs…
90PSI may be low for compression, but as others have said, the small combustion chamber tends to create inaccurate compression gage readings…
When was the last time this thing ran/idled OK? Has it been sitting for a long time since it last ran/idled OK? Did you lend it out, has it been overheated?
Generally speaking, when these things are "worn out", they are hard starting, won’t idle, and are low on WOT power. But, on the other hand, I don’t want to condemn this powerhead just because it won’t idle right…There may be a fuel/ignition problem.
I guess I would try a different compression gage first…The long hose on many testers can be enough to lower the compression readings. If you confirm the 90 PSI readings as accurate, you may want to pull off the head and exhaust cover (provided this is not a salt water engine) to have a look at the piston skirt/rings/cylinder wall. Trying to find a lower pitch prop to solve this issue is probably not going to work out, there is no smaller pitch prop available. But, on the other hand, be sure no one has substituted a larger pitch prop for a 3-4hp engine, which may indeed be overloading the engine….
Generally speaking, trying to "rering" these engines is not an effective repair, the piston skirts/cylinder walls are usually out of round requiring boring the cylinder oversize along with oversize piston and rings. I don’t recommend doing this major rebuild on this little powerhead.
The lower bearing/seal could indeed be leaking causing a crankcase leak, but this would not explain the lower compression reading….