Okay, here's the deal.
Sounds like the oil pressure relief valve spring cound be hanging on the lip of
the spring retainer cap.
Take the cap off and chamfer the hole the spring goes into. Check for burrs on
the inside of the cap and also check the spring to see if it is bent or
deformed in any way.
(Shoots to top of yellow arc - 90 psi. I think all Lyc's do that.)
I dont think so. The oil pressure is generally higher when cold, 5 to 10psi or
so, and comes down to normal gradually when warm but does not jump suddenly.