Ok lets try a couple of things that Rockman was having you look at as well. Check to see where the fuel line feeds into the carb, that entire brass post gets loose once in awhile. You want to be very careful not to overtighten this due to the possibility of stripping that at the base of the carb. There is a nut portion on that stem, hold that firm and attempt to hand tighten it to see if that has become your source of the air leak.
Something else you could try is actually blow through the fuel line connected to you pipe and attempt to push the fuel through the system, while your doing this check to see if you can hear or see air leaks, if you get nothing at all then we have a blockage somewhere and that is when I would investigate the fuel filter or something in the middle of the line.
Let me ask you are holding your finger over the tip of the pipe while turning over the engine as this will help aid in priming the system and you can typically see fuel moving through the lines at this point.
Take the air filter off and hold you finger over the carb and this will give you the same effect as priming the system from the pipe, but it is sometimes easier if to see the fuel come through that way. either way will work. good luck and let me know