Help needed on Walkera 38#

I have a Walkera 38#, (tandem coax with Chinook body, 450 size).

Problem is that I can't get it to work. I can get it to bind under 2401 protocol only, the elevator and aileron work but I can't get the throttle to work. It uses the RX-2409 receiver with an external esc for the 4 brushed motors.I have tried all sorts of settings, all to no avail. Does anyone have any suggestions, any help appreciated.

Also this is my first post so please tell me if I have posted in wrong area

Hi FDR,

Sorry to ask but what is ESV?

I have tried calibrating throttle by moving throttle stick to full range after heli binds. I have also tried setting throttle range to 0-100 instead of -100 to +100 and both these together.

I forgot to add that I am using a Devo 8s.
Thanks for the help, I will keep trying

Hi FDR,

You sir are a genius.

I just set the throttle scale to -125 +125 as you suggested.

Worked perfectly. I would never have thought of that, so simple.

Thanks for the help, much appreciated