If you look at the
picture from Gray Ghost above, that is looking at the throttle shaft and plate from the underside up. The throttle plate is mounted on top of the shaft, if you look from the top down.
From what I can see zooming in on your throttle plate arm, it is definitely different from the other pictured YF2100S carbs posted. Very good probability that the throttle body is not correct for the YF2100S main body (or someone installed the wrong throttle arm/rod when rebuilding). Not surprising considering how some rebuilders just grab what they think are the right parts and assemble/sell without being sure all are correct.
You may need to search for/purchase another rebuildable or parts carb to scavenge the correct throttle body to put everything where it belongs and functions correctly.
