While serving in Viet-Nam, '66-'67. lighter fluid became almost impossible to find at the PX because of black-market activity. A buddy refilled his Zippo with JP-4 (high-grade kerosine used as helicopter fuel and oddly enough in our multi-fuel trucks.) The Zippo worked just fine on this. When lighter fluid once more became available, he let the lighter burn until it used all of the JP-4 then refilled it with lighter fluid. Strangely. it wouldn't work with the lighter fluid. He even tried drying out the 'cotton' fluid holder. Still wouldn't work. So, he went back to using JP-4.