its either the needle seat or a plugged vent....unless the bowll is leaking.....it looks like you need to get in to that carb and fix it..shut the fuel off or clamp it with a couple of vicegrips and take the bowl off.....gas will go everywhere...so get some nitrile rubber gloves......are you up for it?..........this might help. http://www.youtube.com/user/donyboy73#p/search/26/Z3DLNguqLRk