Here's my method for setting up a throttle linkage.

1. With the linkage disconnected from the carb turn your radio on
2. Move your throttle stick to the middle position. Check that your servo arm is now approx. perpendicular to your linkage
3. Manually set your carb to mid throttle
4. Attach linkage to the carb making sure the carb stays at mid throttle, you may have to shorten or lengthen your linkage to achieve this. Now your stick should be at half throttle and so should your carb
5. Set your end points now and you should be good to go or pretty darn close!