Park 300 does not start by themself

I have just purchased 2 Park300 Turnigy Brushless Outrunner 1600kv from you.
The problem is that the engine does not start by themself, I have to manually turn the propeller (GWS 7x3) for it to spin up (same on both motors). I use Turnigy Plush 10amp Speed Controller and have tried with both 2 and 3 cells LiPo. What can be the reason?