If you're using pre-punched cartos, it's very likely that the hole is too small to let a thick (50%VG+) juice through very well, and you'll continue to get the carto running dry. From what you're reporting it sounds like it's doing fine with the juice you put into the carto directly, then just not drawing enough from the tank.
I seem to have an issue with PG, so I've been
vaping 100%VG in cartos for over a year now. I need to double punch my cartos, with holes that are dramatically larger than the tiny ones that are on the
smoktek pre-punched cartos, etc. Every punching tool I've tried (screws,saddle valve ones, impact ones which require a hamer) makes much larger holes, so I'm not doing anything special there. I tend to get 20-30ml through them before I notice a decline in vapor or flavor and switch to a new one.
The carto hate and "can't use VG in cartos lol!" is strong here, but I've had no issues (apart from Bogegate, and even that ended up leading me to the Ikenvape Fusions, which are lovely).
For reference, the pre-punched cartos with a tiny hole, that look like
this flanged one (altsmoke image) do not like thick juices.
Cartos punched with a punching tool like the one
here (vipvaporcig) have holes that are much larger, and punching two holes on opposite sides lets cartos work just fine with thick 100% VG juices, in my experience.
Note that juices vary in thickness for reasons apart from just %VG - I've had some 70/30 juices that are thicker than most of my 100%VG ones - so even some higher-PG juices don't play nice with the tiny hole in many prepunched cartos.
Before I punched my own cartos, I used the prepunched ones from Vaporescence for a while - they were double-punched, with the larger holes. It's been a while, however, but if they're still like that, you have an option if you want to avoid punching yourself (although punching them is super easy. I'm currently using the Siam Mods carto punch, and even a fool like me can't screw it up).
