Carburetor Adjustment; Rocker Arm Clearance - Troy-Bilt TB490BC Operator's Manual

CARBURETOR ADJUSTMENT
The idle speed of the engine is adjustable. An idle
adjustment screw is reached though a hole in the top of
the engine cover (Fig 50).
NOTE: Careless adjustments can seriously damage your
unit. An authorized service dealer should make
carburetor adjustments.
Check Fuel
Old fuel is usually the main reason for the unit not
running properly. Drain and refill the tank with clean,
fresh unleaded fuel prior to doing 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 airifueI 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
WARNING: The cutting attachment may be
spinning during idle speed adjustment. Wear
protective clothing and observe all safety
instructions to prevent serious personal
injury.
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.
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 engine cover
(Fig. 50). 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 e turn at a time (as needed), to reduce idle speed.
idle Adjustment Screw
Checking the fuel, cleaning the air filter, and adjusting
the idle speed screw should solve most engine
problems.
If not and:
• 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: When the unit is turned off make I
sure the cutting attachment has stopped [
before the unit is set down to prevent serious
persona njury.
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 the first 10 hours of operation
and then every 25 hours of operation thereafter.
• The engine must be cold when checking or adjusting
the valve clearance.
• This task shouId be performed inside, in a clean, dust
free area.
1. Remove the muffler cover by pressing down on the
comer with a flat blade screwdriver (Fig. 51). Slide
the notches on the sides of the muffler cover over
the tabs on the engine cover and remove
/
..... Fig. 51
2, Remove the two (2) screws on top of the engine cover
with a flathead or T-20 Torx screwdriver (Fig. 52).
Engine Cover
Top View Of
The Engine
Fig. 52
Muffler
22