Congrats on the new bike.
Cool thing about the 300 is that you can ride them like a 4 stroke, lugging down low.
With regards to the leaking gas, you will need to set the float height on the carb.
The should be a tech article somewhere for it here or you can look at the Keihin US website site.
http://www.keihin-us.com/am/tuning/
WOT
Kim