After working to repair, tune, and just plain set up CAS guns over the last 15 - 20 years, I have yet to encounter a factory Main Spring that was "too light." The exact opposite has been the case in every case.
As posted by 45Dragoon, there are extenuating circumstances (didn't know I knew those big wurds?). Drag and interference. If you look at the sides of the hammer at this point, you may notice scratch and scrape marks from the hammer dragging in the frame and in the hammer channel. Attention from a fine stone may be called for.
Having the incorrect caps for your particular guns as mentioned by Pony Express can also cause you grief. If your Jervous and Nerkey about the amount of pressure seating the caps, you've probably got the wrong caps for your guns. I am also NOT a fan of the OEM nipples. I change out the nipples on EVERYTHING to SlixShot. Then I run Remington #10 caps. Although, just for fun, I'm gonna piddle with a tin of Remington #11s. See what happens.
As mentioned by 45Dragoon, the amount of energy soaked up by the Trigger/Bolt spring and excess drag in the lockworks can also bring one to tears trying to get a Cap Gun to run. A set of small Diamond Files can go a long way.
Hopefully, you won't have to "Start from Scratch" setting up your guns. If you do however, the reward of a nice running Cap Gun is sweet indeed.
Oh, almost forgot, also take a peek at where the Arbor joins the hammer channel. Look for shiny spots that need to be dressed down for full hammer travel.
Coffinmaker