NSR250RG (MC16) - Pre PGM. This uses two CDI units with seperate RC valve control unit.
NSR250R2J or R4J (MC18 '8
- PGM CDI unit. Three additional boxes control RC valve
NSR250R5K or R5K2 (MC18 '89) - PGMII CDI unit. Integrated RC valve control.
From '90 on we all know the story.
I don't have any PGM numbers for the NSR250 R6K and there doesn't seem to be any literature out there. So I have to fail on that one. Maybe the R6K is the dodgy one?