C152 INSTRUCTOR AND STUDENT HAD THE ENG QUIT.

Narrative

ON APR/XX/99 I WAS FLYING WITH A PRIMARY STUDENT IN A C152 APPROX 12 MI W OF ANN ARBOR; MI; ARPT AT 3000 FT MSL REVIEWING AIR MANEUVERS INCLUDING MCA; STEEP TURNS AND THE STALL SERIES. I WAS IN THE PROCESS OF DEMONSTRATING A PWR-ON STALL. AS I RAISED THE NOSE OF THE C152 THE ENG BEGAN TO DETONATE THEN CEASED OPERATING WITH THE PROP IN THE VERT POS. I CHOSE AN APPROPRIATE FIELD IN WHICH TO LAND; THEN WENT THROUGH THE RESTART PROC SEVERAL TIMES WITHOUT SUCCESS. FINALLY; I TOLD THE STUDENT TO PRIME THE ENG WHILE I ENGAGED THE STARTED. THE ENG STARTED AND WE RETURNED TO BASE. IN A DISCUSSION WITH THE SCHOOL'S MECH WE AGREED: 1) WHEN GLIDING AT THE BEST GLIDE SPD OF 60 KTS THE PROP DOES NOT ROTATE AND FUEL IS NOT METERED FROM THE CARB SO THE RESTART PROC WILL FAIL. 2) THE CESSNA POH FOR THE C152; C172 AND C182 CALLS FOR THE PRIMER TO BE IN AND LOCKED IN ENG OUT CIRCUMSTANCES. 3) UPON DISASSEMBLY; THE CARB WAS FOUND TO BE IN GOOD ORDER. THE FUEL WAS DRY AND CLEAN WITH NO POLLUTANTS IN THE CARB. 4) THE PROBABLE CAUSE OF ENG FAILURE WAS A STUCK FLOAT VALVE INTERRUPTING THE FUEL SUPPLY TO THE ENG FROM THE CARB.