Thanks for the comments and the pictures. I've ordered the tail piece of the stock muffler that vibrated off from YS Engines. I'm also going to fabricate a straight pipe in conjunction with threaded header that is still on the engine. Also, I believe that the prop that I was using (APC 15 x 6) might be the wrong prop for this engine, allowing it to rev too high (i.e. 9,500 rpm). I'm going to give a 14x10 APC prop a try.