Technical Information · issue 5 of 2010

Service Note – Always Start Engine in Starting Throttle Position; Adjusting the Carburetor

IssueTI 5/2010

Full text

Page 1 of 3

STIH)

Technical Information 05.2010

STIHL HS 81, 86 Hedge Trimmers – Series 4237

Contents
1. Service Note – Always Start Engine in Starting Throttle Position
2. Adjusting the Carburetor

1. Service Note – Always Start 1.1 Starting the engine
Engine in Starting Throttle
1.1.1 STIHL HS 81 – Starting throttle position
Position
If the engine is warm, STIHL HS 81, 86 hedge
trimmers can also be started without being in the
starting throttle position. In unfavorable operating 1
conditions (e.g. using poor quality fuels, at extreme
ambient temperatures, operating at different and
alternating altitudes) the engine may start normally
but stall as soon as it is accelerated.
2
4
Therefore, always start in the engine in the starting
throttle position to ensure trouble-free acceleration 3
444TI000 KN

after a warm start.

. Set the stop switch (1) to I.
. Depress the throttle trigger lockout (2) and pull
the throttle trigger (3) at the same time – hold
them in that position.
. Press in the starting throttle button (4).
. Let go of the throttle trigger lockout, throttle
trigger and starting throttle button. This is the
starting throttle position.

Go to "Setting the choke lever" (see
chapter b 1.1.3).

TI_05_2010_30_01_01.fm englisch / English
)m~ge 2 Technical Information 05.2010

1.1.2 STIHL HS 86 – Starting throttle position 1.1.4 Cranking
. Crank the engine (see instruction manual).
. As soon as the engine runs, open the throttle
1 wide, the starting throttle button pops out
(HS 81) or the slide control moves to the run
3 position F (HS 86) and the engine can return to
idle speed.
STO

If the engine stalls when it is accelerated even
2 though it has been started in the starting throttle

444TI001 KN
position with the choke lever on e:
. Move the choke lever to g.
. Depress the throttle trigger lockout (1) and pull
. Start the engine again.
the throttle trigger (2) – hold them in that
position. . When the engine begins to fire, move the choke
lever to e and continue cranking.
. Move the slide control (3) to START and hold it
in that position. . As soon as the engine runs, open the throttle
wide, the starting throttle button pops out
. Let go of the throttle trigger lockout, throttle
(HS 81) or the slide control moves to the run
trigger and slide control. This is the starting
position F (HS 86) and the engine can return to
throttle position.
idle speed.

Go to "Setting the choke lever" (see
chapter b 1.1.3).

1.1.3 Setting the choke lever
444TI002 KN

. If the engine is warm, move the choke lever
to e.

TI_05_2010_30_01_01.fm

Page 2 of 3

Technical Information 05.2010 Page 3

2. Adjusting the Carburetor 2.3.2 Procedure

The running behavior of STIHL HS 81, 86 hedge 1. Adjust engine speed to 3,200 rpm with idle
trimmers may react very sensitive to carburetors speed screw (LA).
that have not been adjusted properly. 2. Turn the low speed screw (L) clockwise or
counterclockwise to obtain the maximum engine
The following description produces the best speed.
possible carburetor setting.
If this speed is higher than 3,600 rpm, start again
with step 1.
2.1 Standard setting with limiter cap on the
high speed screw (H):
3. Use the idle speed screw (LA) to set the engine
Low speed screw L: Open 1 full turn speed again to 3,200 rpm.
High speed screw H: Open 3/4 turn (no further 4. Set the engine speed to 2,800 rpm with the low
than stop) speed screw (L).

If engine acceleration is not yet satisfactory
2.2 Basic setting without limiter cap on the
. Use puller 5910 890 4501 to remove the limiter
high speed screw (H):
cap from the high speed screw (H).
Low speed screw L: Open 1 full turn
. Carefully screw the high speed screw (H) down
High speed screw H: Open 1.5 turns onto its seat.
. Open the high speed screw (H) 1.5 turns.

2.3 Adjusting the carburetor . Check acceleration and, if necessary, open the
high speed screw (H) another 1/8 turn at a time
until acceleration is satisfactory – but no more
than 1/2 turn.
2.3.1 General
. Install a new limiter cap.
. Depending on the fuel used, running behavior
may vary.
. Set the specified engine speeds within a
tolerance of +/- 200 rpm – the engine speed
reacts sluggishly to rotation of the adjusting
screws, but even slight adjustments result in a
noticeable change in engine running behavior;
turn the adjusting screws only a little at a time,
then perform a test run and readjust if
necessary.
. Adjust the carburetor with the tip of the cutting
attachment pointing down at the ground –
leanest position of carburetor.

TI_05_2010_30_01_01.fm

Page 3 of 3

Extracted from the manufacturer's 2012 service catalogue. Most of these PDFs embed fonts with a shifted character map, so the text above was recovered rather than copied — read it as a faithful but imperfect transcription, and treat the page image above each block as the authority where the two disagree — the figures exist only there, because they are vector drawings that text extraction cannot keep.

Report a transcription error →