Depends on how one definds the word re-build. To me, rebuild requires parts. Replacement parts for these injectors are VERY hard to get/find.
Just about everyone of these China/Jinma injectors I have had in my hands that were not firing correct have been due to trash or pop off pressure out of spec. Most of the time I can clean and set pop off pressure.
Takes a lot of hours to wear out a injector or Lack of lube in the fuel.
Ronald