Do you have a "sleeve" (sometimes called a "skirt") around the bottom where the tank attaches to the battery? I've found that if that is screwed up too tight to the tank it blocks the airflow and makes it hard to draw. That sentence doesn't make a whole lot of sense, but if you have one, you'll figure out what I'm talking about.
i thought this was going to be your problem, but im glad you got it fixed. ive herard of tank sleeves/thread covers not having the right sized air vents for the nova.