I purchased a back action hammer gun with a Jones underleaver. In the past the leaver has loosened and the owner at the time put a small band of leather on the arm so it would bind with the floor plate and keep it in position. I stripped it down but can't really figure out how to tighten the leaver. Any suggestions?

1. Bend lever.
2. Weld a "catcher" on the trigger guard and file to fit.
3. Get another piece of leather.
That's all I got...Geo

Sounds like it needs a proper fix, not a quick fix. Unfortunately the cure probably isn’t going to be as simple as a bend this, tighten this pin or add a shim here, etc.
As strong as a Jones underlever action is, they do get loose. Sounds to me like you’re going to have to build up the cams on the underlever and make sure that there is adequate bite between the cams (bolt) and the barrel lumps.
Some jones underlevers were snap actions, aka there’s a spring in the action that keeps the lever in place, most of the medium to lower grade actions relied entirely on friction between the cams/bolts and the barrels lumps. It should not be a difficult fix to get the mating surfaces to bite. A little laser welding and some good fitting and it’ll be ready for the next 100+ years of service.

Tamid,
The lever-over-guards in my collection have raised metal on both sides on the bottom
of their trigger guards. Such an arrangement can be seen on Steve Nash's most recent
addition to his pinfire thread (page 29). They keep the lever centered under the receiver and only minimal effort is required force the lever over one of them to open the action.

Thanks for all the advice

Long live the Jones underlever!

Right on Joe,
I too am a fan of the Hammer manual Jones. I love the way you can really feel every bit of those bbls getting screwed down so tight. Not great for flurries, but so what?
I bet it's a pretty dance to watch, with a good shooter with his loader & a pair of Jones actions
cheers
Franc