Tight Draw on a new Boge f15 Carto

[cocacola31173]

I have been using these cartos and I find that sometimes the draw will become very tight on some of them overnight. i am priming them all the same way. I fill them with about 30 drops and let them sit for about an hour and then I put them in the tank and let it sit for about 30 minutes. I dry pull a couple of times before I start using it for the first time.

Is it just the quality of the carto or is there a way I can fix this?

Thanks!