Originally Posted by Mtracer

When you say it is immediately losing air, do you just mean it starts to deflate. Or in a matter of moments it is deflated?

I recently switched a wheel back to tubeless, It was a Bontrager wheel that uses the Bontrager rim strip rather than tape. I used what I thought were the original valve stems. These just would not seal well where they interface to the rim strip. The tire would completely deflate in say an hour. The air was leaking into the rim and finding its way out around the spoke nipples.

I then used some Muc-Off valve stems I had and these came with three different rubber seals for the stems. I used the one that was just a cone shape. So, it sort of fit into the hole. Sealed well, problems solved.

If it's deflating really fast, like a whoosh of air, then probably something is wrong with your methods. Are you having a massive brain fart and inflating without a valve core and forgetting that as soon as you pull the inflator off all the air will rush out the valve? Like I said, it would take a massive brain fart to not figure this out for yourself, but we all have those moments from time to time.

Off course, there's always a chance you have a defective tire. Unless of course you are certain the air is coming from the stem somewhere. And if it is the stem, there's really only two options Either the stem doesn't seat properly inside the rim (my problem), or the valve core is not sealing. Perhaps not properly tightened.