I’m not familiar with a Super Custom 56, but here is a typical procedure that works for most two strokes.

To set the high speed needle, start the engine with a fairly rich setting. Open the throttle all the way. Lean the mixture until the RPM peaks and begins to drop off. (If you go too far and the engine quits, back out the needle about ½ turn and restart.) Peak the RPM and back off a little. You want the high speed setting to be a little rich of peak.

To set the idle mixture, retard the throttle until the engine is operating as slow as it will idle, which may be pretty fast if the adjustment is very far off. Pinch off the fuel line. If the engine dies suddenly, the idle mixture is set too lean. Richen the idle mixture and repeat. If the engine gives a burst of speed before it quits it is rich. Lean the mixture a little and repeat. As you approach the proper mixture, the engine can be set to a lower idle without stopping. As the idle speed is reduced, repeat the procedure until when the fuel line is pinched off at idle, there is a slight increase in RPM before the engine dies. The final test is if the engine accelerates smoothly from idle to full throttle.

There are two types of idle mixture adjustments. One adjusts the fuel flow and is generally a small needle with a screwdriver adjustment opposite the high speed needle and centered in the throttle arm. The other adjusts airflow through a bleed hole and can be located on the throttle body. The needle type turns clockwise to lean while the bleed type turns counterclockwise to lean. If you think the engine is badly out of adjustment, you can get in the ballpark as follows. If it is a needle type adjustment, attach a line to the fuel inlet and close the throttle completely. Blow gently through the line and close the idle mixture adjustment until you can’t blow, then open it a little. If it is a bleed type, look in the hole and adjust the screw until the end of the screw covers half the hole. These procedures will get you to a good starting point.

After you have made these adjustments, with the throttle wide open, raise the nose of the plane vertical. If the RPM sags, richen the high speed needle until it runs smoothly then just a tad more. The nose up attitude lowers the tank well below the intake and tends to lean the mixture. As the tank empties it will lean it a little more. It probably won’t be necessary to change the idle mixture.

Finally, don’t expect to get a dependable idle down too low. Somewhere on the order of 2000-2500 rpm is reasonable.