Obviously Sassee's suggestion is the right way but on some you'll find that the hole that the stud fits through is all worn out. At that point, tightening up the nut has no effect as the spring / washer that should tighten against the window channel to apply friction just passes through the window channel.
Mine was like that and I made a little washer (limited space) that helped but didn't solve the problem. I'll have to take another look at the problem, I'm leaning towards drilling out the hinge and replacing it with a bolt and ny-lock nut to put tension on the hinge instead of the pivot.
I make mention of this as it would be too easy to tighten the nut, check, tighten the nut until you broke it off as mentioned not realizing it is having zero effect on the tension.
:idea: Rethinking...no, it was not that the hole was worn out allowing the spring to pass through. The hole was worn out allowing the enlarged shoulder on the window post to pass through! Same results, it was tightening up the spring and washer on the stud without sandwiching the window frame to apply tension.