It's a long time ago but I recall writing in a carb thread that the Mikuni pilot jets were longer than the Tekei ones and didn't fit properly although they actually worked
See http://ttr250.activeboard.com/t46618273/help-pilot-jet-differences/
Hey Kman, I think we've had this conversation before but Benjah recently bought and used a 52.5 mikuni pilot jet - he confirms it fits and works well in this thread.
I've been looking for a larger pilot jet to replace my size 50. I've just ordered one of these through an outfit called Rocky Mountain ATV, cost me around NZ $10 including delivery so not bad.""