Remove the top of your carb carefullly so you don't lose the spring. Lift the rubber diaphragm out with the needle and slide assembly. There should be some sort of needle retaining screw down inside the assembly. Remove it and push the needle out. Does it have an "E" clip and notches cut into the needle? If so, it's adjustable just like aftermarket carbs. You can then adjust the amount of fuel delivered by moving the needle up and down by installing the E clip on different motches of the needle.
Clip on the highest notch puts the needle deeper into the main jet and reducing the amount of fuel.
Clip on the lowest notch raises the needle and allows more fuel to escape from the main jet.
This does slightly affect your take off, but it's generally the mid to upper RPM that this affects.
It's normally your air mixture screw and pilot jet that affects low RPM and take off, but the needle can affect it some.
This is actually a decent explanation of what is going on.
http://forum.highlifter.com/Basic-CV...-m1872049.aspx