The cap seals the fuel tank of the Good Luck chainsaw. It usually has a pressure-equalizing channel so that fuel flows freely to the carburetor.
Replace it if fuel leaks, the seal is worn, the body is cracked, or the saw stalls because of vacuum in the tank. When replacing, check the tank neck.
After replacement, check the unit at idle and under load: there should be no leaks, play or unusual noises.
