Easiest way to do all that is to turn on your radio and turn on the airplane so the servos will center. Have the throttle stick and it's trim centered when you do this. Then turn off the RX and then the TX (in that sequence).

Now roughly set the length of the connecting rod so that when it's connected to the servo arm and the carb arm, the servo arm will be at 90degrees and the carb arm will be halfway from full open to full closed. Now plug the connecting rod into the carb arm at the farthest out hole. And plug the connecting rod into the servo arm at the hole that's next to the hole that's closest to the inside.

Turn on the TX and then the RX and look at what happens to the throttle arm when the servo arm is centered. Remember to have the throttle stick at center and it's trim lever at center. The servo's centering won't change, but the throttle arm might not still be in the center of it's full-to-closed throws. Keep your TX's throttle stick at dead center and it's trim at dead center. Adjust your connecting rod length so that the carb arm is centered. You want the servo to be centered with it's arm and the connecting rod making a 90degree angle, and you want the carb arm holding the carb halfway open..... or halfway closed if you think that way.

Now move your throttle stick full up and full down. You want the carb to open fully and also close to the perfect idle position. (But since the engine isn't running (it isn't is it? grin) you're not going to know if the setting is the perfect idle position.)
If the carb isn't opening and closing enough, then change the connection on the servo to use a hole that's further out.
If the carb is opening and closing too much, you might hear the servo buzz or see the connector rod bow. Move the connection on the servo to use a hole further in.

If you think the carb is opening and closing "close enough", you can use your radio to fine tune it's End Points so that the carb opens and closes perfectly.

there is more..........