Got a cougar with a magnum 32 engine.

Also fittled is a throttle pipe, any suggestions what size of prop is best for fun fly 3d stuff. I tried 10x7 and it was a bit to fast on idle. Dont have many props in the workshop that might be of use to try so going to have to invest in some new ones, so I was wandering has anyone else done the hard work for me with some research.

Many thanks