The PM650 had a very peculiar problem, would not oil correctly...changed the new pump for a good used one, still pumping air. I decided it must be the pick up hose connection so I tore it all down again, hose, pick up, and clamps were fine, still pulling air. Finally I tried to pressurize the line to see where it was leaking and there was a flaw in the crankcase bottom casting right above the pick up nipple, looked almost like someone had tried to punch a hole there. I drilled & tapped for a short set screw, installed it with red LocTite and problem solved. That only took 4 or 5 hours more that necessary.
Mark