Ah. Sorry.
Try taking the cart apart. The 510 mouthpeice, as provided with both the titan and the yeti, has two rings inside it. The first one you take in your mouth, and the second one is inside the first. Beyond the second ring you have a pair of channels leading to the atmo.
So your needle would need to go in the first ring, then pass through the second, turn left, then turn right, and go forward to get close to the atomizer.
This design REALLLY helps you avoid getting juice in your mouth.
As to the 910, the 20 gauge needle I got from JC won't fit through the slit in the cart, unless you remove that part (Which I sometimes do by accident by biting down and having it pop out) or get a much much smaller needle.