Fuel tank cap

[Dead Eye]

I'd go with Fazerider on this one. Double check the breather hoses underneath the tank - there shouldn't be any real pressure build up in the fuel tank. If this is occuring its likely you're getting low pressure after a long ride on a cool day and that can lead to fuel starvation...

It's a quick job, and the idea of poking something down the breather tube is probably a good idea, just dont use anything too sharp