SER FAQ: LMFAQ: Lawn mower too loud

S.E.R. FAQ

NotTaR of small Gasoline Engines and Rotary Lawn Mowers : Lawn mower too loud
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Lawn mower too loud

Small engines - especially those on cheaper mowers - are usually loud, no question about it. However, if yours sounds like it is about to explode or take off, there may be something actually wrong.

Obviously, if it is backfiring every other stroke, you have a problem with the ignition timing, mixture, valves, etc. What this section deals with is just the normal noise assuming the engine runs properly - and how to reduce it. Else, you need to perform the proper maintenance first.

Make sure everything is tight - it may be the engine rattling against the deck or something simple like that.
Your muffler could be worn out - probably rusted out. Inspect it and if in doubt, just replace. They only cost $3 or so.
Some lawn mowers discharge under the deck. This should reduce the noise level but the proper (probably spark arresting) muffler must be used or else you risk igniting dry grass or whatever as you mow!
It may be possible to purchase an after-market quieter muffler - check with the suppliers listed in the section: Mower and engine parts sources.

Note that for a 2 stroke engine, the muffler is particularly critical for proper operation and substitution may be more difficult.