The generator of a Coleman lantern is a small metal tube inside the lantern's glass cylinder that controls the brightness of the lantern's light. Fuel flows through the generator to the mantle, which is the part of the lantern that produces light. A dirty or damaged generator can prevent the lantern from working properly. You may occasionally need to change the mantle completely if cleaning is not effective.
Light the Coleman lantern outdoors. The process may vary depending on which lantern model you own, but generally you push a lit match into the lighting hole at the base of the lantern and open the fuel valve to the "high" position.
Open the pump knob by turning it counter-clockwise, then pump the knob 15-25 times.
Turn the pump knob clockwise to close the knob.
Turn the fuel valve from the "High" position to the "Off" position several times. This will burn off any residue on the generator tip.
Coleman recommends replacing the generator if you experience difficulty adjusting the brightness of your lantern.