I've never played with the 300's power valves, since I own a 200.
However, my brother has used the power valve adjustment quite a bit on his 300. I don't know which way adjusts for low end vs. top end, but I know it is a very responsive adjustment.
Turning it in (again, not sure of the direction) let's the motor kick you in the butt when it goes on the pipe. Turning it out softens the hit and adds some low end.
Either way, the 300 has huge power, so you might just have too much engine for what you are comfortable with.
I don't know if the manual explains how to adjust the power valve, but try turning the adjustment screw (a little brass screw on the lower right side of the engine I believe) 1/2 turn at a time to see how it reacts.
'01 KTM 200 MXC, '03 Yamaha YZF600R, '97 Honda Shadow Spirit 1100