72 318 Scamp. Low oil pressure 1 minute after startup.

I'm thinking junk on the pickup screen as well, what does the oil pressure do if you rev it up a bit after the pressure at idle goes way down? Does it pick up quickly or take a while to build pressure? Also what's the max pressure it hits when warmed up? Could also be the oil pump is just worn out.

BTW what weight of oil did you put in?