(quoted from post at 20:33:18 06/07/17) If it were mine...
I would not go into it at this time. Those engines are not known for having good oil pressure. If the gauge is showing "some" oil pressure at hot idle, and coming up to 15-20 when up to speed, and no strange noises, it will run a long time.
How is the oil? Any chance it gas been contaminated with gas? Running too rich, flooding carb, clogged air cleaner (there is a wire mesh above the oil cup that is often overlooked), can contaminate the oil.
What kind of oil? The most popular oil in use now is 15w-40 diesel oil.
The pressure relief valve is rarely to blame. Increasing the spring strength will not raise idle or low RPM oil pressure.
The oil pumps on those are not the best. Trying to repair one usually doesn't do much, it is the housing that wears. If you want to go in after the pump, I would recommend replacing it over repairing the old one. However, the new one will be aftermarket, the quality could be questionable.
Again, "if it were mine"...
Check the oil condition, change if in doubt, go with 15w-40 diesel oil, make sure the carb is right, mixture is good, thermostat working. Note what the oil pressure is doing at various speeds, watch it for a period of time. If it gets worse, or unusual noises develop. like knocking on cold start, or under heavy load, that would be the time to take action.