I have just had a play and, as I suspected, the control valve works just as well in any one of four different positions, at 90 degrees to each other.
Simply rotate the valve through a complete 360 degrees with some air pressure on the engine to find the position of the valve that best suits your needs. One you have located your preferred neutral position your servo should be set to its neutral and the two arms joined together. The servo should then operate the engine giving full control in speed and direction.
Edited By Richard Simpson on 21/08/2020 16:55:13