1. I use a sheet of flat plastic ... the kind that those plastic "blister" packages that are almost indestructible are made of.
2. Punch a hole with one of those hand paper punches that punches one hole and save the "hole".
click link for photo
https://www.carlmfg.com/medium-duty-single-hole-punch/
3. Put the "hole" inside throttle shaft bushing area.("Hole" keeps shaft from getting stuck to JB Weld)
4. Then as mentioned above use J B Weld to fill hole even with the casting.
5. Powder coating or painting does not affect J B Weld.