Heres a sugestion try a 13x4W (wide prop) just might give you the torque you need. But for all pratical circumstanses you have a decent set up the 4 pitch may not have a lot of bite so it will slow your TR down making them really sluggish to start even hesitant to start. But all I can say is with changing the prop to a wide you need to be certain that your plane is in its "sweet spot" meaning pretty verticle and sustained in that verticle position. Hope this helps.