the reason putting your hand over the air filter intake is because it makes a bigger vaccum pull in the venturi of the carb and therefore draws more fuel up the jets ,so this means the reason the bike wont run is fuel related mate as in a shortage of it, i would say take the carb off and make sure the fuel is good and fresh with no water in it and also make sure the jets are all very clear and not blocked or even narrowed with debris or build up of emulisfied fuel.
adam bike doctor(of milton keynes motorcycle centre)
February 2011