i'm not familiar with your radio........does it have EPA (end point adjustment)?
if not, you can try a servo horn with more throw and adjust from there to get the low and high to a happy medium.
start out with the throttle servo set to center, then connect to your carb and adjust the length so the barrel is in the middle of it's opening.

if you have EPA though it's really simple......you simply add more throw by upping the percentage of your high end travel...........

here is some info, and i'll look for more
http://www.ronlund.com/throttle.htm