Honda HRS21 Owner's Manual page 37

Spark Arrester Maintenance (Optional Part)
m If the mower has been running, the muffler will be very hot.
Allow it to cool before proceeding.
1. Remove the two 4 mm screws and remove the muffler cap.
2. Remove the spark arrester and gasket from the muffler protector. (Tak-
ing care not to damage the wire mesh.)
3. Check for carbon deposits around the spark arrester, and clean if
necessary.
4. Install the gasket, spark arrester and muffler cap on the muffler protector
and then tighten the two 4 mm screws securely.
4 mm SCREWS
3,5