The airholes for Protanks/Protank IIs are on the base (the part you screw your coil head into, then screw into the
tank) right at the top of the 510 threading. There are 3 of them. You can try plugging one (or more) of these airholes - break off a toothpick inside the hole - to see if that works for you. Smoktech also makes an
Air Flow Regulator you can use to ...duh ...control airflow to the tank.
If you don't care to get a lecture on ohms law, learn the "rule of 2" ...take your coil ohms and add 2 (2.4ohms + 2 = 4.2v), then adjust in .1 increments up or down for taste.