Hi
I have a stiffer one on mine and it works a treat,
A standard one is set up for an 80 kg rider,
I got mine from Splat-shop as he seemed to be the cheapest - http://www.splatshop.co.uk/montesa-stiffer-spring.html
They say if you are over 80 kg put the stiffer spring on,
Also you are meant to have your shocked serviced regally and re gassed
I would have it serviced and the new spring put on
Im from up North so i cant say where to have it done im sorry.
Thanks