If theres enough material there, helicoil it, if not fill the hole with JB weld maybe and re-drill and tap? Maybe plug the hole with the next size bigger bolt SAE or Metric, cut off the bolt flush, drill and tap to the next size smaller than the carb bolt, grind down the threaded end of the carb bolt and rethread it to the next smaaler size to fit the new thread in the main body.