GTRAround 1.5 to 2.5 turns on the GT250 but caution this because KR didnt reveal it and heavily discourages messing with the mixtures. And also caution that rear engine likes to run a little richer (a little). hence the 2.5 step staggered fashion of jetting KR did for the 125 and 250 models.
In your pic. Yes it is a breather / overflow to the ground incase bike tips over (falls) or floats act strange and overflowed the carb (in the sense of the word)
Hope that helps.
// Meditation doesn't mean you have to sit still....
