Arty
I do not know your skill level but if the main spring is weak then it can be retempered. Not a hard thing to do. With a torch or a charcoal grill heat the spring to a dull cherry color and quench it in oil (I have used motor oil with good results). Be careful as the spring will be glass hard and will break if dropped. I now use a fine grit sandpaper and polish the spring so I can see the temper color. A toaster oven will work well to draw the temper. Set it to the highest temperature, most likely about 450 deg. Let the spring heat at this temperature for about 1/2 hour and then using the toast button I heat the spring until it turns a purple color. This should be about 700 deg. Shut the toaster off and let the spring cool in it. Reinstall the spring.
Hope this helps as no fancy equipment is needed.

A. J. Palik