Motors misses when warm

[T needs 2 fish]

Hey Guys , i have a 2002 4 stroke yamaha , the engine starts ok , but while idling its ok but the second i throttle up it misses horribly, it sounds like it back firing through the air cleaner and gets worse the warmer the engine gets , does this sound like a head gasket or valves , or is it something simplier ? Need help , Need to get out and fish.......

 

[robert graham]

Has the carb ever been removed and cleaned?....