Sounds like a leak. The volume put out by the pump is not adjustable, the pump runs when the engine runs. The 009-012 series oil pump works using crankcase pressure changes to move the pump diaphragm (there's an air channel from the crankcase to the port where the pump flange bolts to the case). The rod from the back of the diaphragm pumps the oil. There's a check ball to prevent backflow.
The pump has a foam filter over it, the foam disintegrates when wrong oil is used. Then grunge can gum up the back spring and hold the check ball open.
On the later 012's and 011's there is a plunger button on the pump flange face to help prime the pump, with a seal around the plunger. This can leak.
The plastic pipe from the inner end of the pump to the oiling outlet is submerged in the oil tank. The oil pipe may be have come partially off the pump, or cracked or split there or along the line, or the ferrule at the outlet may be damaged or gone as said before. Oil can leak if these things happen.
The holes for three small screws that hold the pump flange go through the case and open into the oil tank. If these screws are loose, or gone, oil may leak under the flange gasket.
The tank vent is a hole through the case near the top of the tank with a small cotter pin in the hole. This hole is next to the cover stud. Oil can leak out through there. Oil tank can get pressurizerd by crankcase heat, oil can blow out this hole.