Despite the fact that I have been busy preparing and packing gliders for our slope fest next week, I have been thinking about possible designs for a simple muffler.
As this engine will remain soft mounted, it means that the muffler must only be fastened to the cylinder head. That is how the original saw muffler is fastened; just by the two 5mm bolts into the cylinder head.
What I have in mind, with no proper understanding of the theory involved, is to make an aluminium one, round cheese shaped and with two concentric cylinders capped with a removeable round cap. The outlet, or "stinger" as it appears to be called, could be out of the back of the outer cylinder. The inner cylinder is perforated with multiple holes. Between the two cylinders, pack stainless steel scrubbing matt materials, more or less densely. This of course will slowly coke up and restrict exhaust. However, the removeable cap (held on with 3 or 4 screws), would allow it to be removed and replaced as required. The inner perforated part of the muffler would prevent the stainless from possibly going back into the engine, with catastrophic results.
I will do a small drawing of it in LibreCad when I get the time.