RedactedNarrative: Owner had purchased vessel on August 31st and it was the 1st time on the water and it was still registered to previous owner.  He stated he had done a little work on it in his driveway but the boat and engine appeared to be good condition.  He checked the fill tubes, hoses, vents and gas tanks and everything appeared to be good condition.  He filled the boat up with fuel at a gas station prior to launching.  He and his girlfriend were about a mile offshore and he smelled gas fumes in the bilge.  He decided to turn around and head back to shore but soon after turning he heard an explosion and the engine caught on fire.  He attempted to put out the fire, but it re-ignited after the cover blew off the cabin.  They jumped in to the water and were picked up by another vessel.  Neither were wearing life jackets and did not have time to grab them.