Originally Posted by
seliment
(on a Stihl), check that the intake filter in the oiltank is clean, and also check that the air intake valve on the tank is clean. It often looks like a disk about 6mm in diam with small hole in centre and is near the bar mount. It contains a small spring loaded ball which acts as a valve to let air into oil tank as oil is pumped out.
If it's blocked (closed), air can't get in & oil flow will stop. If it is stuck open with a bit of crud, sawdust etc, air will get in all the time and saw will leak oil all the time. Clean by flushing with petrol & compressed air. Stihl service man describes some tests to diagnose oiling probs.
If it's not a Stihl, I don't know the detail of how they should work.
Joe