LT80 petcock explanation

I have a repair manual, but not an owners manual. I can rebuild it completely from the ground up, but i can't turn the fuel on.

From what I've gathered, the petcock is vacuum-operated in one position, free-flowing in another position.

I'm not looking at it right now, but I recall a third position. I'm thinking ON, PRI, and RES.

Someone give me the complete tutorial on this thing.

you are correct, On & Res are vaccum operated, Pri is primer,for free flo

Is the reserve the same scheme as the larger ATVs, a lower pickup tube?

yes