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One thing I have to be careful of.-I mix a bit of 2 cycle oil with my gasoline, for the sake of my Viton o-ring on the piston. None of my small engines run hot enough to burn this oil, so there is a steady fog of oil mist coming out the exhaust. I have to arrange things so there is not an oil trap built into the muffler.
If you look back at some of the threads with Grahams Alyn Foundry engines in them you will see similar exhaust pots being used.