SMA SUFFERS LOSS OF ENG PWR WHILE AT LOW ALT WITH TRAINING IN PROGRESS.

Narrative

WE WERE ON AN INSTRUCTIONAL FLT; PRACTICING BASIC MANEUVERS INCLUDING GLIDES; CRABS AND WING LOW XWIND APCHS AT ALT (APPROX 2300 FT AGL TO 1000 FT AGL) IN AN AREA USED AS THE PRACTICE AREA FOR THE LCL FLT SCHOOL THIS AREA IS VERY SPARSELY POPULATED. AFTER IDENTIFYING OUR EMERGENCY LNDG AREA (YUBA ARPT; A GRASS STRIP) WE BEGAN PRACTICING RECTANGULAR COURSES; CLBS AND GLIDES. WE THEN BEGAN TO PRACTICE GLIDES ALONG A STRAIGHT ROAD IN PREPARATION FOR TRAINING IN XWIND LNDGS. WE WERE GLIDING DOWN FROM ABOUT 3500 FT MSL (2800 FT AGL) ALONG EHT ROAD. CARB HEAT WAS ON. THE DAY WAS RELATIVELY HUMID. WE CLRED THE ENG DURING THE FIRST ONE THIRD OF THE GLIDE WITH NORMAL RESPONSE. UPON REACHING APPROX 1000 FT AGL; WE ADDED PWR TO CLB OUT FOR ANOTHER RUN. THE ENG DID NOT RESPOND TO THROTTLE ADVANCEMENT. AFTER ESTABLISHING BEST GLIDE AIRSPD; I TURNED TOWARD YUBA; OUR DESIGNATED EMER LNDG STRIP. WE RAN THE EMERGENCY CHKLIST; AND BY PUMPING THE THROTTLE REGAINED MINIMAL PWR. I PULLED THE MIXTURE CTL TO LEAN; AND IMMEDIATELY ADVANCED THE CTL TO FULL RICH AGAIN; PREPARING TO LAND; BUT GIVING THE ENG ONE MORE CHANCE. AFTER 2 MORE THROTTLE PUMPS; THE ENG CAUGHT -- DEVELOPED FULL PWR; AND WE CLBED OUT WITHOUT FURTHER ENG DIFFICULTY. MY ONLY HYPOTHESIS HERE WAS THAT SOMEHOW WE HAD FOULED THE PLUGS (SINCE THE ENG WAS DEVELOPING MINIMAL PWR) AND THAT THE LEAN MIXTURE ALLOWED THE FOULING TO BURN OFF PRIOR TO ENG PWR DEVELOPING. WE THOUGHT THAT OUR ENG CLRING PROC WAS ADEQUATE; BUT PERHAPS NOT.