Confused here too, Matt. FCR is the type of carb, I've figured that out.
I thought RFS was a quality term: regardless of feature size. Stuff like surface finish, concentricity, etc.
82 fj40, 99 uzj100, 06 gx470
05 525EXC, 01 XT225, 09 TTR125, 07 TTR90, 07 CRF50