Hi max" ,the CDI"s [OEM] are ok, am running the original , i had the Rex speedshop settup. and it failed , [ its him that says the old cdi"s are crap] , i told him it failed ,and his only reply- "weve done an upgraded version" ,so i said trade the old one against one,= No reply,
So, back to the carb,,change the jet setter,[immulsion tube] and needle, as if they are worn ,more fuel get sucked thru ,. what colour was the plug ? ,,,
Read this. see what i mean ,
https://yamaha-enduros.com/index.php/forum/performance-improvements/7305-rex-s-electronic-ignitions