I don't have that particular engine, but I do have a bunch of SuperTigre's.

Put loc-tite on the muffler circle that plugs into the header, then locktite the retaining screw(s) as well.

Run the engine to warm it up, then tighten the retaining screws yet again.

Remember that as the engine gets warm, things expand, making the bolts and screws fit more loosely.... so it behooves you to tighten things up with the engine warm.
Also check the engine cap screws with the engine warm as well.