I picked up a 1973 World Voyageur yesterday that came with a Middlemores stretched leather saddle. The saddle is alarmingly soft and loose, the complete opposite of the Brooks Professionial that I've been riding most of my adult life. It'll just about bottom out on the seatpost adjuster bolts, and is very pliable. Is it time to start messing with the adjuster nut? I don't want to kill the poor thing.

Use the adjuster. If it rips, so it goes. Very few saddles have any value if they are not both comfortable and usable.

Sounds like this thing is in 'got nothing to lose' condition, so maybe you should try reshaping it first, then tensioning it. (search-engine the term "blocking a bicycle saddle" and you'll find several different articles on the subject)

You guys are right. Wish me luck!

This is one of those threads where I did not want to be the first to offer bad advice! Which is not to say the above is bad.

You are at point where you don't want to do anything that will kill a saddle that may already be dead. If it is as soft as you say, there is probably not much strength left in it. So tension may help, or it may just rip it apart.

Either way, I expect this piece of leather is going to tear into two pieces in another couple hundred miles and there ain't nothing you can do about it. Either hang it on the wall as art, and preserve it as is; or ride it and maybe kill it.

If you do kill it, please send me the remains That said:

I suspect the best you can do is cut a piece of firm foam to fit as neatly as possible between the leather and the rails, and stuff it in there. This will support the leather from underneath. And it can do no harm.

Adding tension would be a little more radical. It may, or may not, work.

Even more radical would be to melt beeswax into the leather. That will harden it for sure, but I question whether the leather can take that heat.

A little update here:

Tightened the adjuster a bit... stopped before I thought I should out of caution. I've got a few dozen miles on it an it seems to be doing well so far. No tears or obvious stress points, and is quite comfortable. It's pretty "wingy" and could probably do with a lacing but it's not causing any significant issues.

thanks for the advice!