Yamaha's have a small bolt up by the head (both my wr and old ass wr have it) that you remove to check for oil flow after changing the oil, I believe its like a 6mm bolt, not sure thread pitch, but I bet you could use it as a test port with a mechanical gauge if you really wanted to, although no spec is given, its just a matter of you should have oil there within a few moments of starting it. These bikes don't require a lot of oil pressure, just an out of my ass estimate probably less than 15psi.