Iwent drag racing last night and noticed that my bike was sputtering and slightly down on power, it acted like it was running out of gas, so i topped it off just to make sure and it still did the same thing, but if i put it on reserve it will run fine and it will run fine in the (on) position if i am just cruising around but when i run it hard it falls on its face what could this be.

 

It's easy to get the on/off/reserve switch wrong.Up is on,down is reserve,middle is off.I still make this mistake all the time

Trash/garbage in tank?

 

might have some crud stuck in the petcock...happened to me with a dirtbike once