Just taken Bonty Jones XR tyres off my old wheels to put on my new 719s. I've cleaned them, wrapped them with 2 layers of decent 18mm electrical tape, cut a hole and put the valve through, cleaned the tyres, popped them on, filled with a cup and a half of Stan's, popped the remaining tyre on, sponged on soapy water around both sides, stuck a CO2 cart on, pumped up and emptied the cartridge. Used 3 carts and got a bit annoyed so put my tubes in.
I also tried a track pump.
Short of going up the garage and using the air line, the only thing I assume is that pre-used tubeless tyres stretch a bit?
Any ideas, oh learned ones?