If it is an MDS .48.......this is what you need to do..........
Close the throttle all the way. Gently turn the low-speed needle in, 'clockwise', until you meet some good resistance. DON'T crank it in , or you may do some damage.
Now, with the throttle still closed, open the low-speed needle 2 1/2 turns 'counterclockwise'. You will need to watch the blade of the screwdriver as you turn it to count the turns. This is a good starting out setting.

When setting 2-needle carbs to run, ALWAYS tune the high-speed needle valve first for optimum performance and rpm. When you have this, THEN play with the low-speed needle to set the transition, not the idle.

If the carb has an 'idle stop screw', turn it out as far as you can w/o it falling out, you don't really need it. Set your idle by adjusting your linkage to the throtle arm so you have the smallest opening in the carb throat as necessary to keep the engine running. You could also use the throttle trim switch on the radio to do this. My MDS .40 idles great with the opening in the carb at only about 1mm from being closed completely. My low-speed (I like to call it 'transition' needle) at 2 turns.

I set-up my throttle linkage, radio throttlr trim lever in a way that allows me to cut the engine totally for shut down. By moving the throttle to idle, then moving the trim lever to full down, kills the engine.