Ok, I think is the end of my gurgling nightmare with kayfun v4. After many tried builds and experiences, I had just tried putting a 1,2 coil in the thing, and play with the wattage (it was the only thing I didn't done). Conclusions : if I don't push it above 12W (3,8-3,9V) it will not gurgle. This might be due of the quantity of vapor being produced in the chamber, and the little airflow (mtl vaping) isn't enough to get out all the vapor produced, causing the condensation in the center pin. Well, in the end, the k4 rocks. Not as much as my squape, but is a fantastic device.
"Bad news" is that I just had put the k4 working properly, and the K5 will be out soon [emoji23]