If you want to create a tapered helix with variable pitch, the following may be helpful for you. I searched and searched for a way to do it and I couldn't find a solution, until I was playing around and found a way. It is quite a simple method, but I hope I can save people some time with this post.

First, sketch a circle on a plane. In "Features" under "Curves," select "Helix and Spiral." Select the circle that you sketched, and in the Property Manager under Parameters pick "Variable pitch." A small table will appear under Parameters. You can modify the pitch of the helix at either end, as well as its diameter, by changing the values under the "P" column and the "Dia" column, respectively. The numbers can be changed directly on the drawing as well. The diameter of the circle you sketched remains fixed, but it can be modified within its sketch. The "H" and "Rev" columns allow you to change the height and the revolution, but you need to first select "Height and Revolution" in the pull-down menu under "Defined As" in the Property Manager.