Always setup your throttle servo arm and carb arm to use only about 60-80degrees of arc. And make sure that when your throttle stick is centered, the throttle servo is centered and the carb arm is centered. And you want the pushrod to be 90degrees to both.

If you setup the throttle system that way, you'll minimize the rotary-to-push-pull problem. And in fact, the two characteristics shown above will actually sort of cancel each other out.