Usually I think the start settings is about 1.5 turns out from main needle. Then basically once warms start from there and test it out, and turn it out 1/4 of a turn and test out, 1/4 turn and test out etc, and then find the point where the engine runs best and the 1/4 turn added gives no performance gain. When you find this point turn it in 1/4 of a turn again to the last place.

If that doesn't work could be the carb needs cleaning. If the shift point is also set quite low so then it goes straight into 2nd gear, it could be straining the engine. Check the shift point first then mixture