Ryobi 990r - Manual (Page 20)

20
MAINTENANCE AND REPAIR INSTRUCTIONS (Continued)
4. Start the engine and let it run for three (3) to five (5)
minutes with the throttle trigger fully squeezed.
5. Release the throttle trigger and let the engine idle. If
the engine stops, turn the idle speed screw (Fig. 40)
n (clockwise) 1/8 turn at a time (as required) until
the engine idles.
6. Final High Speed Mixture Needle Adjustment:
a. While squeezing the throttle trigger fully, set the
high speed mixture needle at the optimum setting
(Fig. 41). See “Definition of Optimum Setting” on
page 21.
7. Final Idle Speed Mixture Needle Adjustment: Adjust
the idle speed mixture needle for smoothest engine
idle using the following procedure. Do not squeeze
the throttle trigger when adjusting the idle speed mix-
ture needle.
a. Set the idle speed mixture needle at the
optimum setting (Fig. 41). See “Definition of
Optimum Setting”.
b. Turn the idle speed mixture needle out
(counterclockwise) to the rich side of
optimum.
The engine should idle and accelerate smoothly.
This unit is equipped with a diaphragm-type carburetor
that has been carefully calibrated at the factory. In most
cases, no further adjustment will be required.
NOTE: To meet the 1995 California emission
regulations, the carburetor has adjust-
ment needle limiter caps to restrict the
amount of adjustment.
The condition of the air filter is important to the operation
of the trimmer. A dirty air filter will restrict the air flow,
which upsets the fuel-air mixture in the carburetor. The
resulting symptoms are often mistaken for an out-of-
adjustment carburetor. Therefore, check the condition of
the air filter before adjusting the carburetor. Refer to
Air Filter Maintenance.
If the following conditions are experienced, it may be nec-
essary to adjust the carburetor:
• The engine will not idle
• The engine hesitates or stalls on acceleration
• The loss of engine power that is not corrected by
cleaning the air filter, muffler, spark arrester screen or
adjusting the valve clearance
• The engine operates in an erratic or fuel rich condition
The carburetor has three basic adjustments: the idle
speed, idle speed mixture and high speed mixture.
NOTE: The string guard and line spool must be
installed and the cutting line extended to
its full cutting length when making
carburetor adjustments.
Adjusting the Carburetor
1. Clean the air filter if it is dirty. Refer to Air Filter
Maintenance in the enclosed operator's manual.
2. Make the initial settings with the engine stopped.
These initial settings should allow you to start and
warm up the trimmer before making the final adjust-
ments.
Initial Idle Speed Setting: Back the idle speed screw
(Fig. 40) out (counterclockwise) until it does not
contact the carburetor throttle lever. Then turn the
screw in (clockwise) until it just begins to move the
throttle lever; then continue turning 2 full turns.
3. Initial High Speed Mixture and Idle Speed Mixture
Settings: Turn both the high speed and idle speed
mixture needles halfway between the allowable
movement of the limiter caps.
CARBURETOR ADJUSTMENT
Throttle
Lever
Fig. 40
Idle Speed
Screw
High Speed
Mixture Needle
Idle Speed
Mixture Needle