Whats this small nut/screw on the back of the OS muffler for? I thought it was there so you could change the direction of the exhaust but before I yank on this thing (it doesn't want to move) I just wanted to be sure.

There is a bolt that runs all the way through the muffler. Should be a lock washer and a nut on the outlet side.

If you want to change the direction of the exhaust--loosen the nut and then take a screwdriver to the front side and loosen the bolt.

Rotate the exhaust outlet where you want it and then re-tighten the bolt with the screwdriver. Now hold the bolt with the screwdriver to prevent it from turning and then re-tighten the bolt real good.

rcpilet is on the money the nut is a lock nut to keep the screw tight

Check the nut again after you run the engine. They are bad about coming loose and loosing the back half or your muffler.

Enjoy,

Jim

A drop of thread locker helps too.

If it is a 50 size or smaller, you can take the muffler apart, remove the baffle and pick up some performance. On the bigger motors you loose too much back pressure to push the fuel, on the 50's and under it works well. Plus you pick up a little extra growl.

Do not overtighten the screw/nut. I've been told by O.S. that the main reason that these screws break and the rear half falls off is because the screw is too tight.
When the muffler gets hot and expands it expands more than the steel screw can handle. This causes the screw to snap.
Poor design IMO but what you have to deal with. Myself, I purchased a length of all-thread at Home Depot and cut it to length. I then installed metal stop-nuts on both ends and have had no failures since. Others at my field do this successfully too. Not as pretty but functional.

I have used the all-thread. I used double nuts on each end. That way I didn't have to have the tension so great against the muffler and it's resultant expansion. I could jam the nuts together real tight so the deal wouldn't come apart.

Enjoy,

Jim