Pretty much as John suggests ^. It is always easier to check whether it locates ok without the spring in. A lot of older guns with threaded trigger blocks are sometimes hard to locate/start, through years of wear/abuse.
I have found the Webley pistols to be oversprung, in an effort to get a lot of power (relatively speaking) out of the design. If you cut the spring down so it just comes to the barrel pivot hole or end of the cylinder, when it is inserted into the piston, you will hardly notice the power drop and you will have the bonus that it will be easier to cock, your trigger will be better and your sear will last longer.