Carburetor Adjustment; Rocker Arm Clearance - Troy-Bilt TB4BP Operator's Manual

Fig. 26
7. Reinstall the air filter cover. Position the slots on the top of the air
filter cover onto the tabs at the top of the back plate (Figs. 24 & 28).
8. Swing the cover down until the tab on the air filter backplate
snaps into place in the slot on the air filter cover (Fig. 28).

CARBURETOR ADJUSTMENT

The idle speed of the engine is
adjustable. An idle adjustment screw
is between the air filter cover and the
engine starter housing (Fig. 29).
NOTE: Careless adjustments can
seriously damage your unit.
An authorized service
dealer should make
carburetor adjustments.
Check Fuel
Old fuel is usually the reason for
improper unit performance. Drain
and refill the tank with fresh 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. 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 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.
2. Release the throttle trigger and let the engine idle. If the
engine stops, insert a small phillips in between the Air Filter
Cover and the Engine Cover (Fig. 29). Turn the idle speed
screw in, clockwise, 1/8 of a turn at a time (as needed) until
the engine idles smoothly.
Checking the fuel, 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.
12
MAINTENANCE AND REPAIR INSTRUCTIONS
Fig. 27
Air Filter Cover
Air Filter
Back Plate
Tab
Fig. 28
Adjustment
Screw
Fig. 29

ROCKER ARM CLEARANCE

This requires disassembly of the engine. If you feel unsure or unqualified
to perform this, take the unit to an authorized service center.
NOTE: Inspect the valve to rocker arm clearance with a feeler
gauge after every 25 hours of operation.
• The engine must be cold when checking or adjusting the valve
clearance.
• This task should be performed inside, in a clean, dust free area.
1. Remove the eight (8) screws on the back of the engine cover
with a Flat-head or T-25 Torx screwdriver (Fig. 30).
Remove
Screws
2. Disconnect the spark plug wire.
3. Clean dirt from around the spark plug. Remove the spark plug
from the cylinder head by turning a 5/8 in. socket
counterclockwise.
4. Remove the engine cover (Fig. 30).
5. Clean dirt from around the rocker
Idle
arm cover. Remove the screw
holding the rocker arm cover with a
large flat blade screwdriver or Torx T-
25 bit (Fig. 31). Remove the rocker
arm cover and gasket.
6. Pull the starter rope slowly to bring
the piston to the top of its travel,
(known as top dead center). Check
that:
• The piston is at the top of its travel
while looking in the spark plug hole
(Fig. 32).
• Both rocker arms move freely, and
both valves are closed.
If these statements are not true, repeat this step.
Rocker Arms
Feeler Gauge
Spark Plug Hole
Remove
Screws
Fig. 30
Rocker
Arm
Cover
Spark
Plug
Hole
Fig. 31
Adjusting Nuts
INTAKE
EXHAUST
Fig. 32