The good thing about the FX Pocket is the IPhone app that lets you look at the shot string graphs, etc.
Try backing the hammer spring out all the way and go 1/4 turn in at a time to find where the fps levels out. You should then be close. Have you watched Steve at AEAC's tuning videos? I have watched about five times and it is finally starting to make sense maybe? There is also a good video with Steve and PJ that explains a few things.