This is Curtsey of the:

Pump plunger has no resistance.

How This Part Works:

The up-and-down motion of the pump plunger is supposed to force air through a check valve and into the lantern fount or stove tank. At the bottom of the pump stem is a leather or rubber cup that seals itself against the walls of the cylinder (called a pump cup). With your thumb over the hole in the center air cannot easily get out of the pump cylinder. When you perform the down stroke the pump cup will force air into the tank.

For more information go to our Theory of Operation chapter.

Why it is Not Working Properly:

The problem is usually the pump cup. It will be dried out, or cracked or will have just form-fitted itself to the cylinder. If this happens then air will not be forced down into the fount.

How To Fix It:

You will need to remove the pump plunger from the lantern or stove and repair/replace the pump cup.

Fig 1

Fig 2

Fig 3

First, remove the clip on the side of the pump plunger cap as shown in figure 1. Then pull hard on the stem to remove the pump plunger. Once you have it out open the pump cup up like an umbrella and inspect if for large cracks as in figure 2. Place the open pump cup in a cup of motor oil as shown in figure 3. Let it sit for about an hour or so.

If you have rips, cracks or tears in the leather, or if it is plastic, I recommend you replace either the pump cup or the entire assembly. The pump cup is part number 216-5091. A pump repair kit which has a backing plate and push-on nut is part number 216A5091. An entirely new plunger is part number 242J5201.

Fig 4

Fig 5

Fig 6

Now take your pump plunger out of your bowl of motor oil. Get a rag and wipe off the excess oil from the pump cup end as shown in figure 4. With compressed air, or with your lips, blow through the plunger from the top. This will get the excess oil out of the hollow plunger stem. Now return the pump cup to its regular shape-you'll note it is a litter bigger in diameter now. Approaching it from the side, slip it into the cylinder and over the air stem like in figure 5. Use a fingernail if you need to when installing the pump cup back into the fount as it may want to fold on you. Push the pump plunger down into the cylinder a bit. Now you need to set the cap down onto the fount. When you do this ensure you have the holes lined up and the oil hole facing up. If it goes on but a little crooked you can either take it off and start over or gently grab it with pliers and twist. You may have to tap on it to get it to snug down completely. Now re-install your screws or the pump clip as in figure 6.