Take a medium sized flat head and insert it into the carb throat with the slide raised. Lower the slides down onto the flat head "make sure the flat head is vertical and not horizontal". Once the slide sits on it, adjust the idle screw to that position to keep the slide at that height. Do the same thing to the other slide.
That should get you close to what you need. Adjust the idle screws the same amount on each side to ensure that they are the same.
If you adjust the idle too high, you will be running on the needle instead of the pilot.
Once it is where you want it, the. Adjust your cables to ensure that the slides raise and lower at the same time. Be aware that you can also adjust these too tight and they raise the slides higher than you set the idle screw. Be patient and it will work.