Ryobi 990r - Manual (Page 21)

21
MAINTENANCE AND REPAIR INSTRUCTIONS (Continued)
Rich
Lean
Adjust to
Midpoint
NOTE: If the carburetor adjustments do not help
the unit to run properly, contact your
authorized service dealer.
NOTE: If the limiter caps are removed at any
time, your unit will no longer meet
the1995 California emission regulations
and you will void the warranty.
Fig. 42
2. Remove the muffler and muffler gasket. Discard the
old gasket (Fig. 43).
CARBURETOR ADJUSTMENT
(Continued)
INSPECTING/CLEANING THE MUFFLER
The muffler should be removed every 25 hours of opera-
tion to inspect for excessive carbon build-up. Excessive
deposits around the exhaust ports or exhaust holes will
cause poor engine performance.
Use the following procedure to remove, inspect, clean and
reinstall the muffler.
Removing Muffler
1. Remove the three (3) muffler mounting bolts from the
cylinder (Fig. 42).
8. Final Idle Speed Adjustment: Adjust the idle speed
by turning the idle speed screw in (clockwise) or out
(counterclockwise) until the cutting head does not
rotate. Do not squeeze the throttle trigger when
adjusting the idle speed screw.
Definition of Optimum Setting for Idle Speed
Mixture and High Speed Mixture
Adjustments
Always set the idle speed mixture needle and high speed
mixture needle at the optimum setting. To find the opti-
mum setting, use the following instructions.
1. Turn the adjusting needle out (counterclockwise)
from the preliminary setting until the engine speed
decreases (rich). Note the position of the needle.
2. Turn the adjusting needle in (clockwise). The engine
speed may increase, then it will decrease as the nee-
dle is turned in (lean). Note the position of the needle.
3. Set the adjusting needle midway between the rich
and lean settings, which is the highest engine speed
(Fig. 41).
Fig. 41
Muffler Mounting
Bolt
Muffler Mounting
Bolt
Muffler
Muffler Gasket
Fig. 43