FX Wildcat mark 1(.22) loosing velocity

i have had this gun for a year now and was totally satisfied with its performance when suddenly its velocity dropped from 900 to 450 feet per second at the muzzle. I decided to change the regulator and installed a new Huma imported from Airguns of Arizona USA. with new regulator and all O rings replaced the velocity is not picking up and stays around 500. I noticed while disassembly that its hammer was sticking in its receiver and I therefore polished and cleaned it till it started to move freely in its way. i also replaced the hammer spring with a more rigid one but to no avail. am at my wits' end as I dont know what to do next.......any help is appreciated
 
Yuppyyyyy, I finally managed to solve it. Opening the hammer and connecting rod I saw that hammer's shoulder was scuffed badly as it was hitting the stud on the side of connecting rod every time it was fired. the hammer started to experience slight jamming in its pathway and thus reducing hitting power on the valve. This resulted in drop in velocity that nothing could undo.

I buffed and cleaned the hammer ensuring its free movement and then carefully adjusted the maximum forward placement of connecting rod so as to keep it from hitting the hammer shoulder and bing . Now I am getting 910 fps average with JSB heavies 18 grn pellets with Huma regulator set at 145 bars