VespaCiao.The petcock is the valve which is screwed into the gas tank bottom on most mopeds.He was checking to see if you had it in the `reserve' or `on' or `off' position.If you don't get gas thru the petcock,the filter that fits into it inside the tank may be clogged with debris.Be careful when removing the petcock,as raw gas will go everywhere AND some have reverse(left-hand)threads.Have you checked down at the carb to see if gas is flowing into the carb?Zippy will get back with you ,I'm sure.Fred's guide has all this in it,too.