MTD Series 600 Operator's Manual page 18

Mulching(ifSo Equipped)
Select models come equipped with a mulch kit which
incorporates special blades, already standard on the tractor, in a
process of recirculating grass clippings repeatedly beneath the
cutting deck. The ultra-fine clippings are then forced back into
the lawn where they act as a natural fertilizer.
Observe the following points for the best results when mulching:
Never attempt to mulch if the lawn is damp. Wet grass
tends to stick to the underside of the cutting deck
preventing proper mulching of the clippings.
Do NOT attempt to mulch more than 1/3 the total height of
the grass or approximately 1-1/2 inches. Doing so will cause
the clippings to clump up beneath the deck and not be
mulched effectively.
Maintain a slow ground speed to allow the grass clippings
more time to effectively be mulched.
Always position the throttle control lever in the FAST
(rabbit) position and allow it to remain there while mowing.
Failing to keep the engine at full throttle places strain
on the tractor's engine and does not allow the blades to
properly mulch grass. Ground speed should be controlled
using the speed control lever.
NOTE: It is not necessary to remove the discharge chute to
operate the mower with the mulch kit installed.
i_i WARNING! Never operate the mower without the
discharge chute properly attached.
To operate the cutting deck without mulching, simply remove
the mulch plug by un-threading the plastic wing nut which
fastens it to the cutting deck. This will allow the clippings to be
discharged out of the side of the deck. See Fig. 5-2.
Figure 5-2
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SECTION 5-- OPERATION