Vessel 1 was drifting, with the motor off and six persons on board, when the group decided to go tubing and subsequently attempted to start the engine.  While starting the engine it was reported that it "revved extremely high" at which time the Operator turned off the engine on Vessel 1, checked to assure that Vessel 1 was in neutral, then tried to start the engine again.  As the engine restart was tried the second time, the engine exploded.  The powerhead cover was blown off and landed away from the boat (in the water) and caught fire.  The powerhead cover than sank.  The engine itself was also on fire, which one of the Occupants tried to put out with an on-board fire extinguisher.  This attempt was unsuccessful as the fire extinguisher ran out before the fire was subdued; water was then splashed on the engine extinguishing the fire.
 
Investigation revealed a gas leak in the motor of Vessel 1.Investigation determined that the problem was with the "Shrader Valve", which is a valve encased in rubber rather than metal in the test port which tests fuel pressure in the fuel-injected engines associated with Ficht Evinrude outboard motors.  The rubber becomes fragile and breaks down causing fuel to be leaked, which appears to have occurred in this case.
Bethel