G'day Gary,
If your are using 15% nitro, the OS "F" plug is too hot, put a OS #8 in it & retune, use minimum of 18% oil, you don't state how much is in your fuel.
Tune it like this, start it & run it up to full power, raise the nose of the plane straight up, if it is too lean it will sag & stop, if it is too rich it will pick up lots of revs, you want it to pick up some revs, but not a huge amount, the amount depends on lots of factors, but this will give you an idea.
Your idle mixture should be set so after you have run it to full power to get it hot, take it to idle & pinch off the fuel tube to the carb, the engine should gain just a few revs, before it slows & stops, if it just dies, when fuel tube is pinched, it is too lean, wind the air bleed screw in to reduce the amount of air & thus richening the mixture, 1/8 turn is all you need to move it & retest.