Noah Pomeroy 8day balance wheel mvmt

[senhalls]

I recently bought a Pomeroy movement, eight day, balance wheel escapement. I seek someone with one or intimate knowledge. As I received this , it had a 3/4" wide mainspring. Quite old and quite set. I put another spring in , a 3/4" wide. It's trying to 'ball up' as there is space for a one inch spring. The anchor for the hole end spring is one half inch across the space. I'll put a one inch spring in it, but What is the strength? and length? Thank you for your consideration. I'll add a pic if required.