Keroseneburner

I guess I am going to drain the tank, check the screen and lines…..then it must be the oil pump.  Crud

I put compressed air into the oil tank….it oozed out the filter.  

I bought this thing used…unknown hours or mx history…ran great for a couple of years…Junior was riding it…the engine locked up.  I pulled the cylinder and the piston has seized at the wrist pin.  Bottom end still felt smooth and tight so I replaced the piston, cylinder, wrist pin, etc. fired it up, loosened the oil filter…nothing.  I bled the pump using the vent block off method, still nothing.  Is there anything else to try or do the oil pumps fail in these things?  I hate to pull it, split the case, and figure out it was something else.  Thanks in advance!