Most riding lawn mower engines come with a muffler installed on the engine exhaust port. The muffler forces the exhaust to travel through noise-canceling chambers inside the muffler. The muffler also provides back pressure for the engine so that it can run at its maximum horsepower. Over time, the muffler can crack or the gasket seal between the muffler and exhaust port can deteriorate, causing the engine to get louder. If this happens, there is a fairly easy fix.
Allow the engine to cool down for a few hours before you work on the muffler, as it gets extremely hot while the engine is running.
Locate the muffler and exhaust pipe running from the front of the engine.
Fit the correct -sized wrench on the two bolts holding the exhaust pipe to the exhaust port on the engine and unscrew them. Pull the pipe off and out of the muffler.
Inspect the muffler. Make sure it doesn't have any cracks in it. Over time, condensation can rust out and crack a muffler. Remove the muffler mounting bolts and replace the muffler if it is rusted out or cracked.
Peel the old gasket off the exhaust port. Scrape any debris off with your fingernail. Place the new gasket over the exhaust port. Slide the exhaust pipe into the muffler and tighten it back onto the exhaust port.