MTD MB320BV - Manual (Page 17)

17
MAINTENANCE AND REPAIR INSTRUCTIONS
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 Screw
CARBURETOR ADJUSTMENT
The idle speed of the engine is adjustable through the air
filter/muffler cover (Fig. 23).
NOTE: Careless adjustments can seriously damage your
unit. An authorized service dealer should make
carburetor adjustments.
Checking the fuel mixture, cleaning the air filter, and
adjusting the idle speed should solve most engine
problems. If not and all of the following are 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.
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-inch socket
counterclockwise.
3. Replace a cracked, fouled or dirty spark plug. Set
the air gap at 0.020 in. (0.5 mm) using a feeler gauge
(Fig. 24).
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)
Fig. 24
Idle Speed Screw
Fig. 23
If after checking the fuel mixture and cleaning the air
filter the engine still will not idle, adjust the idle speed
adjuster as follows.
1. Start the engine and let it run at the fast position for a
minute to warm up.
2. Move the throttle control to the idle position 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 (Fig. 23). Turn the idle speed
adjuster in, clockwise, 1/8 of a turn at a time (as
needed) until the engine idles smoothly.
3. If the unit appears to be idling too fast, turn the idle
speed adjuster counterclockwise 1/8 of a turn at a
time (as needed), to reduce idle speed.
Do not sand blast,
scrape or clean
electrodes. Grit in the engine could damage
the cylinder.
WARNING:
This unit will need
to be running during
idle speed adjustment. Wear protective
clothing and observe all safety instructions
to prevent serious personal injury.
Also, DO NOT set unit on any surface
except a clean, hard area while starting or
performing any adjustments. Debris such
as gravel, sand, dust, grass, etc. could be
picked up by the air intake and thrown out
by the discharge opening, damaging unit,
property, or causing serious injury to
bystanders or operator.
WARNING: