The Conti Race King Supersonics and Racesports can be a bit fiddly to get setup tubeless. Here's the procedure I use:
- wash the inside of the tyre with some sort of detergent (dishwashing liquid, CT18 etc.) to get rid of the mold release wax from manufacture;
- rinse and dry;
- mount tyre on rim using tube;
- make sure at least one side is seated on the bead properly;
- deflate the tube, carefully pop one side of the tyre off only and remove tube;
- insert tubeless valve;
- put in a couple of scoops of sealant (about 100ml);
- put tyre back on and inflate - you may need a compressor to get enough air in the tyre to inflate it. You may also need to remove the valve core to get enough flow even with a compressor.
- go easy on the max inflation pressure. You really don't want to go above 40psi when seating the bead. If it doesn't seat up, use some dilute dishwashing liquid between the tyre and the bead to help it seat at lower pressure.
- shake the tyre / lie it on its side, take if for a ride etc. until it seals up. May take several days.