The Pedersoli lever springs are very thick and heavy compared to Shiloh versions.  You might get an extra spring from VTI Gun Parts and experiment with thinning it by judicious grinding.  Another approach might be to try various thicknesses of fiber washers under the spring you have.

My Pedersoli sharps was like this when I got it about 13 years ago.  I made a shim out of card stock.  Folded it over a couple times and used a hole punch to cut a hole halfway into the side of the shim. I loosened the screw and slid the shim in till it hit the screw and tightened the screw back down.  I have used it this way for years.  It has just enough spring tension to hold the lever up when the action is closed.  The block is a lot easier to take out now as well since there isn't as much tension.  The lever operates nicely now.