I ♥ Cute Cats!
Join Date: May 2008
Location: Ames, Iowa ---- 2008 Hondar CBARrr600ArrArr 2008 Kawk 250r ----------- 2007 Triumph Daytona 675
So you are correct. 2 positions. The petcock is what's referred to as a "vacuum operated" petcock. When the engine is running (and vacuum is created in the intake) it pulls a diaphram in the petcock opening it. As soon as you turn the engine off and vacuum is lost the petcock closes.
So while it is on the "on" position, your petcock self-closes. The other position bypasses the vacuum diaphram and locks the petcock open. This is useful for priming your carburetors (hence the PRI marking) if the bowls are completely dry, or draining your fuel bowls. There really isn't any need to have the pickup on PRI unless you've worked on your carburetors. Even after sitting for an extended period of time a couple of extra cranks of the engine to open the petcock is all it takes to refill the bowls.
There aren't 2 difference level pickups inside the fuel tank as with older 250's so once you're out of fuel, you are OUT. There is no reserve.