peugeot speedfight 2 problem, help?

i am having problems with it running, it runs for like 5 minuets then you just get no throttle response at all and it slowly cuts out, at first i thought it was a petrol problem so i took the carb off and cleaned out the fuel bowl and blew out the jets, then i made sure the petrol flow was clear, so there isnt a petrol problem, i then cleaned the air filter, changed the spark plug and i have now tried a new automatic choke, still not running as it should be. any ideas?

thanks very much connor.