The HKS BOV is a "Pull-type relief" design, meaning that the boost pressure acts to keep the valve seated. If everything functioned with the BOV previously, then something has gone wrong, and whatever went wrong may not necessarily be your BOV.
In regards to the BOV, I would check the sensing port and the line attached to it. This style of BOV will not operate properly if the sensing line is compromised (even a minor puncture) or if the line is not properly connected.
The previous posts asking you to check your boost fittings and lines are spot on good advice, as you may have a boost leak in your system somewhere. Also, I recommend inspecting your wastegate assembly (not just the lines), if something is wrong back there, it will affect your ability to make any boost.
Edit: I don't believe there is a user adjustable spring on the HKS BOV. Perhaps you or your advice giver is mistake, as an adjustable spring is often a feature of the other blow-off valve design, "the push-type," which I believe is the most common type of BOV used.
Re-edit: If you do suspect improper operation of your BOV and don't know how to set it up properly, you can always re-install your stock BOV. By doing the switch and testing, that will indicate if your new BOV setup has somehow gone awry.
Good luck.
