THE ACFT COLLIDED WITH TREES DURING A FORCED LANDING FOLLOWING A LOSS OF PWR. THE STUDENT PLT STATED THE FLT WAS NORMAL UNTIL A 'VIOLENT RIGHT YAW' DEVELOPED WHEN THE TROTTLES WERE ADVANCED TO RECOVER FROM A PRACTICE STALL. AS THE CFI TOOK OVER THE CONTROLS AND ATTEPTED RECOVERY A 'SUBSTANTIAL LOSS OF POWER' OCCURRED ON BOTH ENGS. A FORCED LANDING WAS MADE IN A FLD DURING WHICH THE LEFT WING CONTACTED TREES AND THE ACFT WAS ENGULFED IN FLAMES. POST ACCIDENT EXAMINATION OF THE LEFT ENG FAILED TO DISCLOSE ANY DISCREPANCIES. DISCREPANCIES WERE NOTED ON THE RIGHT ENG. 1) THE FUEL CONTROLLER FUEL LINE 'TEE' FITTING WAS CRACKED AROUND 50% OF ITS CIRCUMFERENCE. (DUCTILE OVERLOAD) 2) THE TURBOCHARGER GASKET ON THE INLET SIDE OF THE TURBINE SHOWED LEAKAGE AOUND 70% OF THE GASKET ARE. THE ACFT HAD A HISTORY OF SYMPTOMS OF FUEL VAPORIZATION WHICH SUBSIDED WITH USE OF THE AUX FUEL PUMP AS THE ENG MANUFACTORER SUGGESTS. IT IS UNKNOWN IF THE AUX PUMP WAS USED DURING THIS ACCIDENT.