Ok, my son asked if I have a stove he could use, something smaller than a two(2) burner suitcase that's he's been using. I break out my first "pack stove" that I baught from the base exchange back around 1986. The Coleman 508 has served me well, until now. In the demonstration to show how it worked similar to his suitcase, the check valve failed to cooperate. Attempts to long term soak out the troubles failed. After 2-weeks the inevitable, order a check valve tool. Here's the thing, as soon as it was removed, it works perfectly. No signs of gum, varnish, debris, nothing, works perfectly. So, I rinse the tank, oil the pump and assundry and off we go... Gremlins? AR