Ryobi 790r - Manual (Page 19)

19
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.
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. 40). Turn the idle speed screw in, clockwise,
1/8 of a turn at a time (as needed) until the engine
idles smoothly.
CARBURETOR ADJUSTMENT
The idle speed of the engine is adjustable through the air
filter/muffler cover (Fig. 40).
NOTE: Careless adjustments can seriously damage your
unit. An authorized service dealer should make
carburetor adjustments.
Fig. 40
Idle Speed Screw
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:
• 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. 41).
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. 41
CAUTION: Do not sand blast, scrape or
clean electrodes. Grit in the engine could
damage the cylinder.
WARNING: The cutting attachment may be
spinning during idle speed adjustments.
Wear protective clothing and observe all
safety instructions to prevent serious
personal injury.
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