Abstract: An exhaust valve and a catalyst can be easily disposed of in a simple manner. The interior of a triangular muffler is partitioned into three expansion chambers. A manifold pipe is connected to the second, middle expansion chamber sideways from a lower portion thereof and is accommodated therein so as to face upward. A catalyst is accommodated in the interior of the manifold pipe. Exhaust gas flowing out from an open end of the manifold pipe expands into the second chamber. A short-circuiting aperture is formed in a second separator and is opened and closed with an exhaust valve installed within the third chamber. The exhaust valve is normally closed by a spring. When the exhaust pressure reaches a predetermined magnitude, the exhaust valve opens automatically, allowing the exhaust gas to flow out into the third chamber through the short-circuiting aperture, thereby controlling the exhaust pressure.

Abstract: An exhaust valve and a catalyst can be easily disposed of in a simple manner. The interior of a triangular muffler is partitioned into three expansion chambers. A manifold pipe is connected to the second, middle expansion chamber sideways from a lower portion thereof and is accommodated therein so as to face upward. A catalyst is accommodated in the interior of the manifold pipe. Exhaust gas flowing out from an open end of the manifold pipe expands into the second chamber. A short-circuiting aperture is formed in a second separator and is opened and closed with an exhaust valve installed within the third chamber. The exhaust valve is normally closed by a spring. When the exhaust pressure reaches a predetermined magnitude, the exhaust valve opens automatically, allowing the exhaust gas to flow out into the third chamber through the short-circuiting aperture, thereby controlling the exhaust pressure.