My wife's 172b won't stall either. It just runs out of elevator with a forward
CG. Tough to do full stall landings. It just "plops" in. If you trim it in the
wrong direction you will have more elevator surface but you essentially will be
pressing the tail down with raw muscle. I put a 60lb bag of sand in the baggage
and it became a new plane. Even her instructor commented how much nicer it
lands. The elevator just needs a little help.

Jim