Exmark Metro 21 Operator's Manual page 17

Cut the grass more frequently.
Overlap cutting swaths instead of cutting a full swath
with each pass.
Set the cutting height on the front wheels one notch
lower than the rear wheels. For example, set the front
wheels at 2-1/4 inches (5.7 cm) and the rear wheels at
2-3/4 inches (7.0 cm).
Cutting Leaves
After cutting the lawn, ensure that half of the lawn
shows through the cut leaf cover. You may need to
make more than one pass over the leaves.
For light leaf coverage, set all the wheels at the same
cutting height setting.
If there are more than five inches (12.7 cm) of leaves
on the lawn, set the front cutting height one or two
notches higher than the rear cutting height. This makes
it easier to feed the leaves under the lawn mower
housing.
Slow down your mowing speed if the lawn mower
does not cut the leaves finely enough.
If you mow over oak leaves, you can add lime to the
grass in the spring to reduce the acidity of the oak
leaves.
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