I guess it depends on the set up.  in my case the throttle opens when pushed back (or pulled back) toward the firewall with the throttle arm moving aft.  Unlike other four strokes, you look down from the top to see in to the carb throat in a YS.

I would set it up to run on the test stand and set the throttle in the mid position and start, then move the throttle on the tranny to see what happens.  Be careful as the enginne will be turning over pretty fast.  But that way you can determine the throttle control is reversed or correct.  That is if you push up the throttel on the tranny and the engine accelerates then it is correct.  If you push up the throttel on the tranny and the engines slows down to idle it is reversed. If reversed, then reverse the servo on your tranny and it is fixed.    Use end point adjustment, sub trim or the like to get the travels correct.

Good luck,

Chip