Tama HP900-7H Heavy Tension Spring

The day I got this spring I tightened it as far as my pedal would allow (Iron Cobra Single Pedal). This means that I am going to have to replace it before too long which is rather frustrating. When I first bought my pedal some years ago the spring tension was perfect and I could keep tightening it as it wore. But for some reason the new springs are not as tight. This may or may not be a problem to other users. Also a little guidance on how get a heavy spring on in the first place would be really useful as I had to use a vice.