Replacing The Spark Plug - Troy-Bilt TB90BC Operator's Manual

CARBURETOR ADJUSTMENT
The idle speed of the engine is adjustable through the air
filter/muffler cover (Fig. 42).
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 Screw
If, after checking the fuel mixture and cleaning the air filter, the
engine still will not idle, adjust the idle speed screw as follows:
1. Start the engine and let it run at a high idle for a minute to
warm up. Refer to Starting/Stopping Instructions.
WARNING:
The cutting attachment may spin
during idle speed adjustments. Wear protective
clothing and observe all safety instructions to prevent
serious personal injury.
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 (Fig.
42). 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 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.
WARNING:
To prevent serious personal injury,
make sure the cutting attachment has stopped
rotating before you turn it off and set it down.
MAINTENANCE AND REPAIR INSTRUCTIONS
Idle Speed
Screw
Fig. 42

REPLACING THE SPARK PLUG

Use a Champion RDJ7Y spark plug (or equivalent). The correct
air gap is 0.025 inch (0.635 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.
WARNING:
Do not sand blast, scrape or clean
electrodes. Grit in the engine could damage the
cylinder.
3. Replace a cracked, fouled or dirty spark plug. Set the air
gap at 0.025 in. (0.635 mm) using a feeler gauge (Fig. 43).
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.
TRANSPORTING
• Allow the engine to cool
before transporting.
• Drain fuel from unit.
• Tighten fuel cap before
transporting.
• Secure the unit while
transporting.
CLEANING
WARNING:
To avoid serious personal injury,
always turn your unit off and allow it to cool before
you clean or service it.
Use a small brush to clean off the outside of the unit. Do not
use strong detergents. Household cleaners that contain
aromatic oils such as pine and lemon, and solvents such as
kerosene, can damage plastic housing or handle. Wipe off any
moisture with a soft cloth.
STORAGE
• Never store the unit with fuel in the tank where fumes may
reach an open flame or spark.
• Allow the engine to cool before storing.
• Store the unit locked up to prevent unauthorized use or damage.
• Store the unit in a dry, well-ventilated area.
• Store the unit out of the reach of children.
LONG TERM STORAGE
If the unit will be stored for an extended time, use the following
storage procedure:
1. Drain all fuel from the fuel tank into a container with the
same 2-cycle fuel mixture. Do not use fuel that has been
stored for more than 60 days. Dispose of the old fuel/oil
mix in accordance to Federal, State and Local regulations.
2. Start the engine and allow it to run until it stalls. This
ensures that all fuel has been drained from the carburetor.
3. Allow the engine to cool. Remove the spark plug and put 1
oz. (30 ml) of any high quality motor oil or 2-cycle oil into
the cylinder. Pull the starter rope slowly to distribute the oil.
Reinstall the spark plug.
NOTE: Remove the spark plug and drain all of the oil from the
cylinder before attempting to start the trimmer after storage.
4. Thoroughly clean the unit and inspect it for any loose or
damaged parts. Repair or replace damaged parts and tighten
loose screws, nuts or bolts. The unit is ready for storage.
0.025 in.
(0.635 mm)
Fig. 43
15