so on = when the bike is in normal operation, pri.= primeing of the carb fuel sys. and res.= the reserve portion of the tank should you forget to fill up and your bike starts to die switch to res and it should get you to the nearest service station i believe its .94 of a gallon so dont get to far out. lol and as for fixing take the two screws that hold the switching mech. and plate of which reveals the retaing ring and a very hard to find o-ring below the switch is a 4 port gasket which you can also replace. now if you flip the petcock to access the four flush screws remove and pull that plate it will reveal the vacuum diaphragm which also has a tiny o-ring on the tip and then there is the gasket on either side of the diaphragm . hope that helps my friend