Backfiring misfiring

I have replaced motor recently along with rotor and plugs. twice the fuel spider has been replaced. filter for fuel and air been replaced. started hesitating and now backfiring. had this problem before the rotor cap. jumped sparks inside filed all the plugs and was dumping gas in the exhaust. that was about a month ago. ran fine for two weeks, now it's backfiring again. what is the problem? please help