Coastie: Look at your throttle arm on the side of the carb. In the center, there is a hole there with a screw head depressed inside. That is your low speed needle. Only use small adjustments with this, like perhaps 1/16 to 1/8 turn at a time. With this needle, a little goes a long way. Of course, with a rotating prop, this is best done with the engine shut down.

DS. (also coastie, but retired)