Model 85 problem

[AlbinoAlligator]

I just picked up an older Taurus model 85. The problem it has is that it misfires when shot as a double action. If I manually cock the hammer before each shot it fires everytime. But if I just squeeze the trigger without cocking the hammer first (double action) It fires about one out of five times. I should also mention that the timing/cylinder alignment is fine, and the firing pin is hitting the primer everytime. I believe I have ruled out the ammo, as I shot 20 rounds single action, and 20 double action. All the single action rounds fired, and only 5 of the double action rounds fired. And it is not specific to any cylinder hole. Anyone ever have this problem? Or have any idea what the problem might be? I would like to fix it myself if I can rather than send it off and be without for who knows how long. Thanks in advance.
AA

[Luckyducker]

A-gator, a previous owner has either altered the main spring or replaced it with a Wolff or other main spring.   I have a Taurus model 66 357Mag that I put a Wolff main spring in to lighten the action/trigger pull, which it did, but it also caused fail-to-fire in DA shooting.   The spring is fairly easy to change yourself.  HTH

[AlbinoAlligator]

Thanks for the advice. Now all I have to do is find one in stock. Midway usa has the wolf spring kits but it sounds like that did'nt work well for you. Any advice on where to find a main spring for my taurus 85? Numrich is out of stock.