running bad backfire and inlet manifold gasket blown

well my 2l pancake engine started to run a bit sluggish an back fire so we started to remove plugs to check sparks ect and i noticed it blow through inlet manifold so i removed on of my carbs and yes its it blown through.
what caused it?
what should i do next ...apart from buy a new gasket
any help ...ideas would be gratefully accepted

 

What carbs, and which gasket? the one under the carb, or between the manifold and head?

 

solex twins and it was manifold one that seats onto engine

 

probably an age thing dude... unless the manifold nuts were a touch loose?

 

cheers ill change both sides they did seen loose and did look worse for wear a bit like me on a morn its an excuse to strip all my tin wear off and polish it i suppose maybee spray it up nice