How recent is this problem? I mean, was the coil that came preinstalled fine, and now that you are changing coils, you are running into this problem? Were you ever successfully using your tank/coils? It's not unheard of for people to have this problem with smok, IIRC someone else new to the forum was having a similar notaste/badtaste problem.... I think her solution was boiling the coils for 20 minutes, IIRC, they were yukkk or something from the manufacturer, and apparently cleaning them made them work better for her....
That said, priming a coil is important. You need to let it sit 10--15 min and slowwwly dial up the wattage, after taking about 5 heavy pulls on the coil, no fire button. Also, I think IIRC many people using high wattage and coils like that continue pulling from the coil/soaking juice UP into the wick, AFTER they vape, in preparation for their next vape, are finding that their coils continue wicking well. Yours might wick for a little while, then get dry, leading to odd tastes? I do that with my Nautilus coil just naturally (want to make sure I get all the vape) but I don't get dry hits, gurgling, taste issues, etc. It's just a good habit to get into especially with monster tanks/coils that may be harder to wick.
As others have said, you may need to find the sweet spot for your tank, which MAY end up being LOWER than 120, or HIGHER. You don't have to vape a coil TO its recommended wattage, though I wouldn't go ABOVE the recommended wattage for a multitude of reasons.
That's about all I got. Good luck...
Anna