RE: magnum 4 stroke muffler loose
Every four stroke engine I have seen has a screw in header like the Magnum and they can be a pain.
Be sure to screw the jam nuts onto the header pipe as far as possible, as in the picture. Screw the header into the engine until it stops and then back it out only enough to point where you want it. Using high temp permatex rtv or teflon thread tape is a good idea. Tighten the jam nut as tight as you can. Get the engine hot, shut it off, and tighten the jam nut again. That should help it stay tight.
Carrell