Hello; I have some recent information on that subject. A friend "Mike" asked me if I could re-energize his two old Saito engines, one an 80 the other a 45. The 80 ran like a champ right away, easy starts and low idle. The 45 was next, it didn't have the Saito pipe that they come with, but a piece of aluminum conduit with a 3/8" exit. At first I couldn't get it to fire, then the odd cough, then it would run only long enough to burn it's prime, and only while I had the glo heater attached.

I told Mike about the problem, and tried a few other approaches by swapping carbs and pipes. The engine would run fine with my carb and my pipe on it, but If tried my carb with his pipe, it would just run on it's prime and die.

We dicided that the open pipe wasn't providing enough back pressure to keep the glow plug lit on it's own.

I have seen 4 stroke engines run for years without mufflers, and was surprised by this outcome.

Your experiences might differ.