Anyone have experience with one of these? I just got a used 220J off of Craigslist. It lights and runs fine but I noticed that it seems to go dim really fast, about 30 minutes or so. I also noticed that when I pump it up before lighting the lantern, I can hear air being sucked through even though the valve is closed, is this normal?

The guy I bought it from also told me not to pump it while it's lit, saying that it might cause the fire to be sucked in and essentially create a bomb of sorts; but I see people pumping a lit lantern all the time. Is it okay?