I assume you have the kit (not ARF) per your forum posting. It's a great kit and fun to fly plane. As previously mentioned, the kit comes out tail heavy. I have a OS 91 FS up front and does the job well, not great, but has the power to do most everything the plane is capable of. I even tried a Magnum 120 FS up front to change the balance, but it just didn't change much. Reduce weight every place possible (servo's, battery, fuel tank, control arms, etc ...) and a 91 FX or FS should fly it fine.

Back to your question on prop, I don't know, but would bet that you need more power. And good job on the build, there is a lot of building with this kit, but that is what the sport is about: building your own plane!!