I'll assume you aren't a Lawn-Boy addict (like myself). These are mufflers. Lawn-Boy's are two-stroke. Their exhaust ports are on the bottom of the engine and mate up with mufflers underneath the deck. This makes them quiet. The unburnt oil in the exhaust collects in them. You need to clean the exhaust ports every couple years or so (depending on how many hours you put on her) and, eventually, you need to clear out all the unburnt oil that has collected in the muffler itself. The easiest way is to put the muffler in a fire of some sort (propane grill works great) and wait for the flame coming out the hole to die out. The engine lasts practically forever so you can restore your Lawn-Boy to the same power it had when brand new by doing this. My 'daily-driver' Lawn-Boy, 30 years old, was bought by my wife at a yard sale for $20 cause the guy thought it was completely worn out. Cleaned the ports and muffler and she was the same as new (my mower, not my wife, that is)...