The fuel petcock is a negative pressure valve type. When it is in the ON or RES position it uses pressure from the 3rd carb boot to feed gas as needed. When it is on PRI or prime it allowes a continueous flow of gas. There are two outlets, the top is the vacum pipe which goes on the 3rd carb boot . The bottom is the all important fuel line, which goes to the carb. If the fuel is coming from the top you will need to buy a kit too fix it. bikebandlt.com as been more reliable for parts then the nearest dealer but it never hurts to check. Hope this helps and good luck. I´m hoping to get my seca 750 back on the road by the end of next week. It´s amazing how the time flies even when your not having fun.