I run one on a OS 160FX and closed off one of the tubes permanently. Why??? Read the engine instructions. Most all specifically state that you should not use a muffler with an opening bigger then the stock muffler. The Bisson Pitts muffler openings are twice the size of the stock muffler. I couldn't even get the mixture to adjust without closing one off as there is not enough back pressure for the engine to run properly. I crimped the tube farthest from the port with a pair of vise grips right at the box. You can't see it and there is a big enough opening still in it to let any fuel drain out. Engine runs great now. I found the tip in a RC Universe Review.