Ryobi 990r manual Carburetor Adjustment, Adjusting the Carburetor, Air Filter Maintenance

Page 20

MAINTENANCE AND REPAIR INSTRUCTIONS (Continued)

CARBURETOR ADJUSTMENT

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:

Throttle

Lever

Idle Speed

Mixture Needle

Idle Speed

Screw

High Speed

Mixture Needle

•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.

Fig. 40

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.

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Contents 990r Introduction Table of Contents Fuel and PRE-OPERATIONAL Safety WarningsCalifornia Emission Regulations Other Safety Warnings OperationalSaftey Warnings for Brush Blade During USE After USESafety and International Symbols SymbolBrushcutter Safety Installing the Shoulder Strap Assembly InstructionsAdjusting the J-HANDLE Installing the Brush Blade Mark Installing the Line SpoolBlade Locating Removing the Lower Attachment Boom Installing the Lower Attachment BoomOperating Split Boom Coupler OIL & Fuel Information Recommended OIL TypeAdding OIL to Crankcase Initial USE Checking the OILChanging the OIL Recommended Fuel TypeDefinition of Blended Fuels USE of Blended FuelsSTARTING/STOPPING Instructions Throttle TriggerPosition RopeAdjusting the Trimming Line Length Using the Brush BladeOperating Instructions Decorative TrimmingMaintenance and Repair Instructions Maintenance Schedule Frequency Maintenance Required Refer toRewinding the Existing Reel Correct Line to UseRemoving the Existing Reel Bump Knob Inner ReelWinding the Existing Reel Reinstalling the ReelInstalling a Prewound Reel Gear Housing Service Fill PlugAIR Filter Maintenance ScrewAir Filter Screws Choke LeverCarburetor Adjustment Adjusting the CarburetorAir Filter Maintenance Final High Speed Mixture Needle AdjustmentRemoving Muffler INSPECTING/CLEANING the MufflerLean Adjust to Midpoint Rich Inspection and Cleaning Muffler ReassemblyChecking Spark Arrester Screen Torque the screw to 15-20 inlb 1.7-2.2 NmScrew Screws Checking / Adjusting Valve to Rocker ARM ClearanceReplacing the Spark Plug Adjusting Nuts Rocker Arm Valve Flat Feeler GaugeCleaning and Storage SpecificationsCold Torque Specifications EngineTroubleshooting Problem Cause ActionCalifornia Emission Control Warranty Statement Your Warranty Rights and ObligationsLimited Two-Year Warranty

990r specifications

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