you need to jack up the tension in the spring, if you loosen off the bolt at the end of the arm, (that clamps the bar the sprung part is attached to) and take out the bolt that holds the tensioner in place, turn the main arm anti-clockwise, and tighten it. que paint diagram:
you will need to play with how much you turn the arm, if you turn it too much it'll be to much stretching for the spring and it goes weak. it will reduce chain wobble loads and give you better tension