This is almost always a clog or a dull blade issue.
- Empty the grass bag.
- Check that all four cutting height adjustment levers are set to the same position.
- Wash the grass bag if it's clogged with clippings.
- Clean out any debris clogging the mower deck.
If clumps are still being left, the blades are dull, worn, or damaged. Inspect them. A dull blade can be sharpened. A bent, cracked, or excessively worn blade must be replaced as a set. Install only Honda Genuine blades.