MTD YM90 - Manual (Page 20)

20
Replacing the Spark Plug
Use a Champion RDJ7Y spark plug (or equivalent). The
correct air gap is 0.020 inch (0.5 mm). Remove the plug
after every 25 hours of operation and check its condition.
1. Stop the engine and allow it to cool. Grasp the plug
wire firmly and pull it from the spark plug.
2. Clean around the spark plug. Remove the spark plug
from the cylinder head by turning a 5/8 in. socket
counterclockwise.
3. Replace cracked, fouled or dirty spark plug. Set the
air gap at 0.020 in. (0.5 mm) using a feeler gauge.
See Figure 44.
CAUTION: Do not sand blast, scrape or
clean electrodes. Grit in the engine could
damage the cylinder.
4. Install a correctly-gapped spark plug in the cylinder
head. Tighten by turning the 5/8 inch socket
clockwise until snug.
If using a torque wrench torque to:
110-120 in.•lb. (12.3-13.5 N•m).
Do not over tighten.
0.020 in.
(0.5 mm)
Figure 44
Idle Speed Screw
Figure 43
SECTION 7: MAINTENANCE AND REPAIR INSTRUCTIONS
Carburetor Adjustment
The idle speed of the engine is adjustable through the air
filter/muffler cover. See Figure 43.
NOTE: Careless adjustments can seriously damage your
unit. An authorized service dealer should make
carburetor adjustments.
Check Fuel Mixture
Old and/or improperly mixed fuel is usually the reason for
improper unit performance. Drain and refill the tank with
fresh, properly mixed fuel prior to making any
adjustments. Refer to Oil and Fuel Information.
Clean Air Filter
The condition of the air filter is important to the operation
of the unit. A dirty air filter will restrict air flow and change
the air/fuel mixture. This is often mistaken for an out of
adjustment carburetor. Check the condition of the air
filter before adjusting the idle speed screw. Refer to Air
Filter Maintenance.
Adjust Idle Speed
WARNING: The cutting attachment may
spin during idle speed adjustments. Wear
protective clothing and observe all safety
instructions to prevent serious personal
injury.
If, after checking the fuel mixture and cleaning the air
filter, the engine still will not idle, adjust the idle speed as
follows.
1. Start the engine and let it run at a high idle for a
minute to warm up. See Starting/Stopping
Instructions.
2. Release the throttle trigger and let the engine idle. If
the engine stops, insert a small Phillips or flat blade
screwdriver into the hole in the air filter/muffler cover.
See Figure 43. Turn the idle speed screw in,
clockwise, 1/8 of a turn at a time (as needed) until the
engine idles smoothly.
NOTE: The cutting attachment should not rotate when
the engine idles.
3. If the cutting attachment rotates when the engine idles,
turn the idle speed screw counterclockwise 1/8 of a
turn at a time (as needed), to reduce idle speed.
Checking the fuel mixture, cleaning the air filter, and
adjusting the idle speed should solve most engine
problems.
If this is not the case and the following are all true:
• The engine will not idle
• The engine hesitates or stalls on acceleration
• There is a loss of engine power
Have the carburetor adjusted by an authorized service
dealer.
WARNING: After turning the unit off, make
sure the cutting attachment has stopped
before setting the unit down. This helps
prevent serious personal injury.