Different motor start spin

Hello, I’m assembly a S500 drone with 4 motors 920kv and 30A Simonk ESCs. The single ESC calibration (directly to the ch3 receiver) is done 3-4 times. But the result is still as you can see in this video:

The video is taken during the “motor test” procedure with APM 1.3.66 : the second engine don’t start, and the third has a little delay.
This second video shows only the second engine that starts only at the second click of motor test:

And the last one is when the drone is nomally armed with the radio:

Firmware is 3.6.8.
Any idea? Thank you!

Read this…

Soved changing MOT_SPIN_ARM and MOT_SPIN_MIN. Thank you!