martinc,
Take into consideration that most of the people who fail to master the UFS (and sell them) are those who tend to make too large of adjustments in the Juice Control. Thus causing flooding, then they turn it back too far causing dry hits/burned taste. When doing this they keep oscillating around the proper setting without ever finding it.
Another thing to think about is that the Air Control and the Juice Control work hand in hand together. Which means they both have to be adjusted to some extent to control two different variables. For example; each person has a preference to what kind of draw they like. But, a tight draw tends to bring in a larger amount of juice with a smaller adjustment. While an airy draw will bring in less juice with the same adjustment. You also need to take into consideration the variable viscosity of the different blends of juices (PG, VG, H2O, Alcohol, etc). So if you change the blend, the previous settings will not work properly.
When doing the adjustment (after establishing what kind of draw you like),
1.) add a drop or two of juice via the mouthpiece,
2.) adjust the juice control a very little bit, and I mean a VERY little bit.
3.) vape.
4.) if you get a dry hit after a few vapes then repeat steps 1-4 until you find Nirvana.
Ok,in a nutshell:
Upon refilling,close air,close juice,refill--open juice a bit,prime,close it---open air,vape till more juice needed,open juice a bit,adjust to taste,vape away.
10-4