Remove the muffler outlet cover plate by detaching the four hex head bolts, using a socket. Pull the cover off by hand.
Detach the screw that secures the spark arrestor inside the muffler outlet, using a screwdriver. Pull gently on the spark arrestor to remove it.
Scrape back and forth across the surface of the spark arrestor with the bristles of a wire brush until you have removed all the dirt and debris.
Reinsert the spark arrestor and secure it with the screw. Reattach the muffler outlet cover plate and secure it with the four hex head bolts.