Why won't my tubeless MTB tire seat on the rim after setup?

[Nora.G]

I'm trying to convert my mountain bike to a tubeless tire setup for the first time, and I'm having a terrible time getting the tire to seat properly on the rim. I've taped the rim, installed the valve, and added sealant, but when I try to inflate it with my floor pump, the bead just won't pop into place. I've even tried the trick with a burst from a CO2 cartridge, but it still leaks air rapidly around the sidewall. Are there specific techniques for seating stubborn tires, or could it be that my rims and tires aren't fully compatible for a tubeless setup?