27/09,

That's very interesting. I've done spins in at least four 172s and have never had any problem getting them into stable spins, using elevator and rudder only.

I don't remember where the CG was relative to the forward limit, but that can be a significant factor in an aircraft being reluctant to spin. I have extensive spinning experience in Blanik gliders and it was quite noticeable that with a lightweight student in the front seat, the spin was very stable. With a heavyweight (e.g. me) in the front seat, the spin would often turn into a spiral dive, even with the stick back on the stop.