THE FLIGHT INSTRUCTOR AND STUDENT PILOT MADE AN EMERGENCY LANDING IN A RESIDENTIAL AREA AFTER AN ENGINE FAILURE. A COMPLETE ENGINE EXAMINATION REVEALED NO MECHANICAL MALFUNCTION OR FAILURES. THE EXAMINATION OF THE FUEL TANKS REVEALED NOTHING THAT WOULD CONTRIBUTE TO AN ENGINE FAILURE. INSPECTION OF THE FUEL TANKS REVEALED THAT THERE WAS FUEL IN THE LEFT TANK BUT NO FUEL IN THE RIGHT TANK. THE FLIGHT INSTRUCTOR STATED THAT THE ENGINE QUIT IN-FLIGHT SHORTLY AFTER SWITCHING FUEL TANKS.