To remove the the oil pump you must first remove the clutch, clutch drum, and oil pump drive gear the clutch is a L/H thread and needs to be jarred off, there are some cut aways in the clutch to insert a screw driver which you can then tap with a hammer ( do not be tempted to use a piston stop, as this may cause much greater problems than you already have ) jar the clutch against engine compression. Once removed take away the screw holdind the silver bar protection plate, and remove the plate, there is now just one screw holding the oil pump on, once removed the pump will come away, under the pump is the oil pick up pipe and filter. The pump is adjustable, three position, for 13/15/ and 18" bars
Husqvarna man, November 2009