Cub Cadet MTD P90 Series - Manual (Page 88)

P90 Series Vertical Shaft Engines
82
Catalytic converter
On engines equipped with a catalytic converter muf-
fler, there is an air injector assembly on the cylinder head,
as show in Figure 8.7. There is a passage from the air
injector to the exhaust port.
When the exhaust valve is open the gases inside the
engine escape to the muffler at great velocity. The pres-
sure of the exhaust gases will close the reed valve in the
air injector, preventing them from escaping through the
injector. The exhaust gases are forced through the cata-
lyst, which will chemically change the gases to lower the
emissions.
When the exhaust valve closes, the momentum of the
gases keep them flowing out of the muffler. This will create
a low pressure in the exhaust port. The low pressure will
cause fresh air to be drawn in through the air injector. The
fresh air is needed to re-charge the catalyst for the next
exhaust cycle.
NOTE: The catalytic converter is part of the muffler and can not be serviced separately.
To service the air injector:
NOTE: The air injector red valve can become plugged up from dirt, grass, insects and many other things. This
would prevent fresh air from getting to the converter.
1. Remove the two screws that hold reed valve assembly to the cylinder head using a #2 phillips screwdriver.
See Figure 8.7.
2. Clean the reed valve as needed.
3. Install the reed valve.
4. Test run the engine before returning it to service.
Figure 8.7
Air injector