hello again
I know, that as less is drag in exaust, better is performance (not talking about resonance pipes)
but won't engine idle better with bit more backpressure? and won't it have better transacion?
what about needle settings? wwill they become touchy without muffler?

My experience without a muffler on a OS 52 was 200-300 rpm increase. Didn't notice any other changes

I haven't noticed much difference other than richening up the hi speed to provide enough fuel. You may get a rich low end not having the reduced fuel flow at low speeds that the muffler pressure provides.

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.