This is Curtsey of the:
Lantern burns dim.
What it is Not Working Properly:
A lantern requires fuel and air to operate. A dim lantern can be caused of any number of things but it usually indicates a lack of fuel, or, a too-lean mixture. In order or probability, the causes are listed below:
1. Dirty Generator. After much use the generator will start to clog up. At some point it will choke off some of the fuel vapor being applied to the mantle(s). Turn your lantern lever, if it has one, around quickly a few times and watch. Or, turn the valve on and off quickly a few times and watch. If the lantern, at some point in this turning process, gets real bright then your generator is dirty and is about to fail. It does, or soon will, need to be replaced.
2. Dirty Fuel & Air Tube.The source of fuel for the lantern is the Fuel and Air (F&A) Tube. If the lantern sits around for extended periods of time with fuel in it, the fuel will leave a varnish on the brass F&A tube. This will restrict flow and ultimately shut it down completely. To fix it you need to remove the valve from the lantern as the F&A tube is below the valve. Please refer to our Rebuild Instructions to continue.
3. Weak Fuel & Air Tube Spring (Lanterns prior to 1983-ish) . A closed valve means that the F&A rod is bottomed out. The valve is not "hard-wired" to the F&A rod but it does control the rod. When you open the valve up the rod is allowed to move up, thus allowing more fuel to be applied to the fuel and air mixture. The rod moves for two reasons: the aforementioned valve manipulation allows it to occur. Second, there is a spring that forces the rod upward. If this rod is too weak to do its job the rod will not unseat itself properly from the bottom of the F&A tube. This will keep the mixture far to lean for a bright lantern. Like before, To fix it you need to remove the valve from the lantern as the F&A tube and this spring is under the valve. Refer to our Rebuild Instructions to continue.
4. Cracked Fuel & Air Tube Gasket (Lanterns after 1984-ish). The F&A tube in these "newer" lanterns is plastic, has a gasket and has a valve similar to a bicycle tire. This gasket rests between the valve assembly and the F&A tube and seals air from getting in the system from this junction. If the seal cracks from age or over-tightening, way too much air will get sucked into the valve and the mixture will be too lean. Yes, the F&A needs to come out so you'll need to refer to our Rebuild Instructions to continue. The gasket alone is available on this website for most lanterns. But if you're going to take the time to remove the F&A tube I'd probably recommend you replace it too.