If the white needle you mean as in poppet valve (white plastic valve that almost looks like a car engine valve) I usually set with the C pointing toward the spray hole from the primer cap side)
If it is a powertoruqe less than 10 years old, I have found a lot of them have never ran properly except at on full throttle, I have one that I have owned from new at my fathers place that has never been 100%. The new generation powertorque motors are chinese made and I cannot say much about them that is good apart from they seem a lot quietr than its australian older brother.
According to the victa manual you cannot swap the black needle for the white needle but I have not found good reasoning not to. However if the original poppet valve is insterted correctly and the rest of the carb is put together riight it shouldnt make much of a difference.
