Will a 1/3 hp impeller work with a 3/4hp motor?
No it will not. The impeller and motor have to be the same. If you have a 3/4HP motor you need a 3/4HP impeller. If you know what model your pump is, not your motor, I can identify which impeller you need. If you don't have this information you can attach a picture of the pump so I can identify it for you.