Carburetor Adjustments; Adjusting Procedure - Craftsman 358.79828 Operator's Manual

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SERVICE AND ADJUSTMENTS
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CARBURETOR ADJUSTMENTS
.Ca_uretor adjustment is critical and if done imprope_ can permanently damage the engine as well as.the car-
- Durezor. vrease reaa all instructions and consult the Troubleshooting section of this manual before beginning
this process.
If engine does not start, it may be flooded. If in doubt,
read the section on flooded engine in the starting section
of this manual prior to beginning any adjustments.
If you are unsure about adjusting the carburetor or expe-
rience any problem while attempting this procese, please
call the 1-800 number listed on the front cover of th s
manual for further assistance.
The carburetor has been adjusted at the factory for sea
level conditions. Adjustments may become necessary if
, the unit:is used at significantly:higher altitudes or i:fyou
notice any of the Tollowing conditions:
•* Bladeor trimmer head moves when the engine runs at
• Turn idle speed screw ("3") clockwise 1/2 turn.
• Start the engine and operate for ten (10) minutes to
warm up. Go to "Adjusting Procedure.
ADJUSTING PROCEDURE
Engine operating speeds: Maximum operating speed:
11,000 RPM.
IDLE SPEED ADJUSTMENT
: Allow the warm engine to idle.
Adjust the Idle Speed Screw until the engine continues
.... to run without stalling and without the, blaoe _or semi-
automatic head turning.
- Turn screw clockwise to increase engine speed if
enginestalls or dies.
idle speed. See =idle Speed Adjustment." _ . .
_ Engine will not idle. See Idle Speed Adjustment" and - lurn screw counterclockwise ro slow engine Oown
?Low SpeedMixture :AdjualmenL _ .... . an_,ortokeep.:thebladeorb'lmmerh_.d.fro.m_tumi.ng_
Engine dies or hesitates when it-should accelerate:See..- :. r_o mrther adjustments are necessary _ place or ram-
=Acceleration Adjustment." mer head does not turn at idle speed and if peffor-
• Loss of cutting power which is not corrected by air filter .... mance is satisfa_ory.
_ cisan!ng. See =High Speed: Mixture Adjustment."
NOTE_ If the Cutting Attachment rotates during idle; turn
the idle speed adjusting screw ("T") counterclockwiseuntil
the Cutting Attachment stops.
_ CAUTION:
MAKE ALL CARBURETOR ADJUST-
MENTS WITH TRIMMER HEAD ATTACHED.
_0_ NOT ATTEMPTTO ADJUST CARBURE-
TOR WITH BLADE ATI'ACHED DUE TO DIF-
RCULTY OF PROPERLY SETTING CARBU-
RETOR. SEVERE ENGINE DAMAGE
COULD OCCUR.
_ WARNING:
MAKE CARBURETOR ADJUSTMENTS
WITH THE LOWER END SUPPORTED TO
PREVENT TRIMMER HEAD FROM CON;
TACTING ANY OBJECT. HOLD UNIT WITH
YOUR HAND.
THE TRIMMER HEAD WILL BE SPINNING
DURING MOST OF THIS PROCEDURE.
WEAR YOUR PROTECTIVE EQUIPMENTAND,
OBSERVE ALL SAFET_-_PRECAU:TIONS_ ...
IN "LOW SPEED MIXTURE:ADJUSTMENT,".
RECHECK IDLE SPEED,AFTER EACH,
ADJUSTMENT.THE TRIMMER HEAD MUST
; , • , NOT MOVE AT IDLE SPEED.
CARBURETOR PRESETS (Fig. 39)
The Carburetor has three adjusting screws:
L = Low speed mixture adjusting screw
H= High speed mixture adjusting screw
T = Idle speed adjusting screw
If your engine will not start due to suspected improper car-
bt.iretoradjustment, the following presets may be required.
If used, it is recommended that all steps within the adjust-
ment procedure be completed in order to assure a prop-
edy set carburetor. If presets are not needed, proceed to
section =Idle Speed Adjustment."
Very small adjustments can affect engine pedorrnance. It
is important to turn the screw a very small amount per
ad._ustmentand test performance before making further
aojustments. Eacn adjustment should be no more than
the width of the slot in the adjusting screw.
° Turn both of the mixture screws (marked "H" and "L")
- clockwise until they stop. Do not force the screws as
damage can occur. Then, turn each screw one (t) full
turn counterclockwise.
Figure 39
LOW SPEED MIXTURE ADJUSTMENT
• Allow engine to idle.
•Tum the Low Speed Mixture Screw slowly clockwise
• untilthe RPM Starts to drop. Note the position.
Turn the Low Speed Mixture Screw slowly counter-
clockwise until the RPM speeds up and starts to drop
again. Note the position.
• Set the Low Speed Mixture Screw at :the midpoint
between the two pos_ons.
HIGH SPEED MIXTURE ADJUSTMENT
IMPORTANT'DO NOT OPERATE ENGINE AT FULL
THROTTLE FOR PROLONGED PERIODS WHILE:
• MAKING HIGH SPEED ADJUSTMENTS AS DAMAGE
,_; ,TO,THE ENGINE CAN OCCUR.
: '• Make a test cut in grass.
--,, Based on performance of the unit while cutting, adjust
the high speed mixture screw in 1116 turn,increments
as follows:
- Clockwise if unit smokes or loses power while cutting.
Do not adjust for best power by sound or speed, but
judge by how well the unit performs during,operation.
- Counterclockv_se if the unit has speea whilenot cut-
ting, but dies or lacks power whilecutting.
: Repeat the test cut in grass.
Continue with 1/16 turn adjustments until the unit per ÷
formance is acceptable while cutting.
• After completing adjustments, check for acceleration.
• If unit accelerates properly no further adjustments are
necessary. If not proceed to acceleration check.
ACCELERATION CHECK
, Ifthe engine dies or hesitates instead of sccelerating, turn
the Low Speed Mixture Screw 1/16 of a turn at a time
counterclockwise until you have smooth acceleration.
• Check the idle speed for stability and that the blade or
trimmer head does not turn. Adjust as necessary.
• Recheck for smooth acceleration and stable idle.
• Repeat process as necessary for acceptable perfor-
mance.
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