I just filled 4 cartos 'cause I'm goin' on the road tomorrow (job interview 3 hours from here and I don't want to smell like an ashtray when I get there). After I read your post, I got worried and checked 'em. 3 of them were a little bubbly on the 1st draw; I had to draw slowly at first. But they're all OK now.
Is it possible you got some juice on the threads? I'm new at this too, and although I understand the air flowpath through the atty/cart, I'm not really sure of the flowpath for a carto. However I do know the air has to go through the hole at the threaded end, so you have to keep liquid out of it.
To fill, take both condoms off. The one over the threads has a ".... plug" like a rubber thumb tack that goes into the hole at the threads; set that aside. Put juice in the other condom, and slowly push the mouthpiece of the carto into it until you just see juice in the hole at the threaded end. Put the .... plug back into the hole, then put the condom over it to seal the threaded end. Empty remaining juice from the other condom, wipe the mouthpiece off and slide the condom over it. Do the taryn spin (pretty vigorously) so the juice flows toward the threaded end. I got a mouthful of juice the first time I filled a carto. Since I've been doing it this way, I haven't had a problem.
20-second taryn spin with 1.5-foot length of twine has been working for me. If you use something short, you won't produce nearly as much centrifugal force, so you may have to spin much longer than 20 seconds.