AN UNDETERMINED FUEL SYSTEM PROBLEM THAT RESULTED IN A FUEL LEAK, AN ENGINE COMPARTMENT FIRE, AND A PARTIAL LOSS OF ENGINE POWER. A FACTOR RELATING TO THE ACCIDENT WAS: THE LACK OF SUITABLE TERRAIN FOR A FORCED LANDING. AN EXHAUST LEAK FROM THE FRACTURE OF AN IMPROPERLY WELDED BAFFLE TUBE MAY HAVE BEEN THE SOURCE OF IGNITION FOR THE ENGINE COMPARTMENT FIRE.