Jetting for tuned motor?

i am having problems with my malossi 166 motor.
i have just fitted a T5 carb to it (SI24,24G) and
i am not sure what main jet to put into it, i am currently
using a 113 but when i give it full gas it holds back
what size should i be using for best performance?
Cheers to anyone that can help!!!
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