my 44c carbs came with 38s the guy I got them from said the carbs had never been apart so I'm guessing that is stock. I know a couple of other 650 guys that went to after market pipes and they when up to 40s They are running 118s as their main jets. I have stock airbox and stock 4 in to 4. My bike just woke up by going to 105 (from the 120s that came in it) I have a lot of bike shops around here and they will sell me used jets in about any size real cheap. New jets they rip for (like $10 ea)