Spark arresters are common safety features on equipment with motors, as they prevent flammable material from entering the muffler and igniting the exhaust fumes. During normal use of a Ryobi string trimmer or brush cutter, dust, dirt, and other particles get into the system and build up around the spark arrester. If too much build-up occurs, it may block exhaust from venting out properly and lower the product's performance. Ryobi suggests throwing away and replacing fibreglass spark arresters, however metal spark arresters can be cleaned.
Unscrew the screws holding the spark arrester from the muffler to remove it. Their exact location will depend on the model you have, but if you can't find the spark arrester, your owner's manual will have instructions for where it is located.
Spray the spark arrester with a carbon cleaner.
Scrub with a wire brush to clear away dirt and debris, then reattach the cleaned spark arrester to the muffler.