speedfight starts then cuts out after about 1 min

hi guys ,
my friend has a speedfight 2 , it starts for aabout a min and then cuts out , the fuel gose into the carb and the fule filter and after it starts no more fuel is going down the fuel line into the filter and then into the cab dose anyone no what the problem could be or has any suggestions what it could be .

 

poor vaccume off tthe fuel tap or the vaccume nipple might be partially blocked on the carb or maybe as simple as a split vaccume pipe , or a loose one .