What if it's a small leak and at idle thrust isn't enough to fed, or start, a fire? What if advancing the throttle puts enough fuel through to feed the fire and you think it's just a bleed leak???
Shut it down.
At an attempt to decipher this statement, this sort of engine fire has never happened on a jet engine. Fuel pressure is somewhat constant, none the less given the fact it can vary you would experience a constant fire. Retard thrust, bleed will drastically reduce, fuel will burn hard!