Just got a brand new set of Roval SLX 24 and trying to set it up tubeless. They already came taped and with a valve pre-installed, so I put on RBCC tubeless, added stans and inflated with a compressor. The tyre sealed all right, but then the it immedately deflated. I found there is a tiny hole in a rim, right below the stem, where it is losing air. The hole looks "factory made" and it is on both rims. Any ideas what to do about that? Thanks!

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That's unlikely to be the issue. That should be a double-walled rim, so for air to get into that area, you've got a leak around a spoke hole in the rim tape.
Generally, when the tire isn't sealing properly, look for where the Stan's it bubbling out.

Thanks, that is the problem, no Stans coming out, but as soon as I stop pumping, it losses all the air.

I'd bet that the valve isn't screwed tight enough against the rim. They have to be in there fairly tight to prevent leaking around the valve/rim bed seal. I usually tighten it, then pull on the valve while wiggling it back and forth and tighten it some more.

So I just confirmed, put my finger against that hole, the air comes out of there for sure.

So.. then run it with an innertube..

That OEM rim tape is just to protect the inner tube from the spokes. it is not necessarily air-tight. Try some actual tubeless rim tape. it seems obvious that the air somehow escapes through the tapes and the spoke holes in that void between where that factory hole is.

There is a set of plugs, which came with the wheelset. Do you think those would fix the problem?

Not necessarily...some tubeless wheelsets come pretaped with tubeless rim tape...my American Classic wheels did. Since the OP said the valves were included (and preinstalled even) I’d guess it’s tubeless rim tape.

only in your Opinion is is imperfect, sonny. it's just Trendy now.. calling it "better" is Marketing.

We got along fine with inner, tubes for decades, Pro race bike-tires had the innertube sewn in , tire glued on the rim.

The rims are supposed to be 2Bliss ready from the manufacturer.

The plugs are should be sealing the spoke holes and if they are missing, voila, leaks.

Instructions for installing the plugs are at: https://media.specialized.com/suppor...0000045737.pdf

I'd put the plugs in and/or use tubeless rim tape. Should do the trick.

Good luck!

The inner section of the rim is never intended to be air tight, you're noticing air coming from that vent hole because it's the biggest, most open hole in the rim. The leak is either at the rim tape or at the valve.