Hope the Kiwis don't mind me jumping in to the middle of your conversations!

Regarding the original question, 4-stroke engines are a lot less critical as to the need for a muffler and maintining a specific exhaust back pressure than are 2-strokes, so it's not surprising that you and your mate have been able to run well without any muffler. Helicoil is an appropriate solution, and if you have a good race engine shop in the area (I know that there's some, since my wife and I have been to one of the Saturday night short track races on the north island down there!) they can probably do this for you or recommend someone else that can.

As to how to start a new thread, go to the main page of the section on which you want to make the post and click on "New Post" in upper left area and go from there.

Beautiful country with a very interesting history you have, just wish that we had been there longer and also that we had also gone to the south island.