well appart from taking htis engine of your palne and converting it to a paper weight, i would advise that you change to a medium(temperature) plug with that high nitro content you should be running a no.8 not an A3 (which is a HOT plug designed for lower nitro content like 5% and below.

if that doesnt work then i think you have a lemon and should
A. scrap it and buy somthing else
B. send it in again and see if they can spot somting else
C. send it in again and ask them to send you a completly new engine

regards
James