Carburetor Adjustment; Replacing The Spark Plug - Ryobi 790r Operator's Manual

MAINTENANCE AND REPAIR INSTRUCTIONS

CARBURETOR ADJUSTMENT

The idle speed of the engine is adjustable through the air
filter/muffler cover (Fig. 43).
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 be
spinning 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. 43). Turn the idle speed screw in, clockwise,
1/8 of a turn at a time (as needed) until the engine
idles smoothly.
Fig. 43
20
NOTE: The cutting attachment should not rotate when
3. If the cutting attachment rotates when the engine
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
2. Clean around the spark plug. Remove the spark plug
3. Replace a cracked, fouled or dirty spark plug. Set
4. Install a correctly-gapped spark plug in the cylinder
If using a torque wrench torque to:
Idle Speed Screw
110-120 in.•lb. (12.3-13.5 N•m)
Do not over tighten.
the engine idles.
idles, turn the idle speed screw counterclockwise
1/8 of a turn at a time (as needed), to reduce idle
speed.
WARNING: To prevent serious personal
injury, make sure the cutting attachment
has stopped rotating before you turn it off
and set it down.
wire firmly and pull it from the spark plug.
from the cylinder head by turning a 5/8-inch socket
counterclockwise.
the air gap at 0.020 in. (0.5 mm) using a feeler gauge
(Fig. 44).
CAUTION: Do not sand blast, scrape or
clean electrodes. Grit in the engine could
damage the cylinder.
head. Tighten by turning the 5/8-inch socket
clockwise until snug.
0.020 in.
(0.5 mm)
Fig. 44