Stihl Ht 75 Owners Manual

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HT 70, HT 75Standard Setting:Shut off the engine.
:Check chain tension.
:Check the air filter and clean or 
replace as necessary.
:Check spark arresting screen* and 
clean or replace as necessary.
:Check adjustment of the throttle 
cable and readjust if necessary – 
see Adjusting the Throttle Cable.
:Turn high speed screw (H) 
counterclockwise (max. 3/4 turn) 
as far as stop.
:Carefully screw the low speed 
screw (L) down onto its seat. Then 
open it one turn counterclockwise.
:Start and warm up the engine.
:Adjust idle speed with the idle speed 
screw (LA) so that the chain does 
not rotate.Fine Tuning A slight correction of the setting of the 
high speed screw (H) may be necessary 
if engine power is not satisfactory when 
operating at high altitude or at sea level.
* see Guide to Using this Manual”Rule of thumb
:Turn high speed screw (H) about 
1/4 turn for every 1000m (3300 ft) 
change in altitude.
Conditions for adjustment
:Carry out standard setting.
:Warm up engine for about 5 
minutes.
:Open the throttle wide.
At high altitude
:Turn high speed screw (H) clock-
wise (leaner) no further than stop 
until there is no noticeable increase 
in engine speed.
At sea level
:Turn high speed screw (H) counter-
clockwise (richer) no further than 
stop until there is no noticeable 
increase in engine speed.
It is possible that maximum engine 
speed may be reached with the 
standard setting in each case.
Adjusting Idle SpeedIt is usually necessary to change the 
setting of the idle speed screw (LA) 
after every correction to the low speed 
screw (L).
:Warm up engine for about 5 
minutes.
Engine stops while idling
:Turn idle speed screw (LA) slowly 
clockwise until the engine runs 
smoothly – chain must not rotate.
Chain rotates when engine is idling
:Turn idle speed screw (LA) slowly 
counterclockwise until chain stops 
rotating and then turn the screw 
about another 1/2 to 1 turn in the 
same direction. 
Erratic idling behavior, engine stops 
even though setting of LA screw is 
correct, poor acceleration
Idle setting too lean:
:Turn low speed screw (L) 
counterclockwise (about 1/4 turn) 
until the engine runs and 
accelerates smoothly. 
						

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Erratic idling behavior
Idle setting too rich:
:Turn low speed screw (L) clockwise 
(about 1/4 turn) until the engine runs 
and accelerates smoothly.
If the engine is low on power, check the 
spark arresting screen in the muffler.
:Lift spark arresting screen and pull it 
out sideways.
:Clean spark arresting screen if 
necessary.
:If screen is damaged or coked up, fit 
a new one.
:Refit the spark arresting screen.
* see “Guide to Using this Manual”Wrong fuel mix (too much engine oil in 
the gasoline), a dirty air filter and 
unfavorable running conditions (mostly 
at part throttle etc.) affect the condition of 
the spark plug. These factors cause 
deposits to form on the insulator nose 
which may result in trouble in operation.
Spark Arresting Screen* in 
Muffler
392BA035 KN
Checking the Spark Plug
000BA002 KN 
						

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HT 70, HT 75 If engine is down on power, difficult to 
start or runs poorly at idling speed, first 
check the spark plug.
:Remove spark plug - see “Starting / 
Stopping the Engine“.
:Clean dirty spark plug.
:Check electrode gap (A) and 
readjust if necessary – see 
Specifications.
:Use only resistor type spark plugs 
of the approved range.
Rectify problems which have caused 
fouling of spark plug: 
:Too much oil in fuel mix.
:Dirty air filter.
:Unfavorable running conditions, 
e.g. operating at part load.
Fit a new spark plug after approx. 100 
operating hours 
or earlier if the electrodes are badly 
eroded.To reduce the risk of fire and burn 
injury, use only spark plugs 
authorized by STIHL. Always press 
spark plug boot (2) snugly onto 
spark plug terminal (1) of the proper 
size. (Note: If boot has detachable 
SAE adapter nut, it must be 
attached.) 
A loose connection between spark 
plug boot and ignition wire 
connector in the boot may create 
arcing that could ignite combustible 
fumes and cause a fire.
Removing the Starter Cover:Take out the screws (1).
:Remove the cable lug, if fitted.
:Lift the starter cover (2) away from 
the tank (3) and pull it out from 
under the shroud (4).
000BA036 TR
1
Replacing the Starter Rope 
and Rewind Spring
386BA004 KN
1
1
12
34 
						

							33 HT 70, HT 75english
Removing the Rope Rotor:Take out the screw (5).
:Remove the rope rotor very 
carefully.
The rewind spring is seated in the 
rope rotor and may pop out and 
uncoil if care is not taken. 
The pieces of broken spring may be 
under tension and fly apart 
unexpectedly when you remove the 
rope rotor. To help reduce the risk of 
injury, wear face protection and 
gloves.
Replacing the Starter Rope:Use a screwdriver to pry the cap (6) 
out of the starter grip.
:Remove remaining rope from the 
rotor and grip, making sure the 
ElastoStart sleeve is not pushed out 
of the grip.
:Tie a simple overhand knot in the 
end of the new starter rope (see 
Specifications) and then thread the 
rope through the top of the grip and 
the rope bush (7).
:Refit the cap in the grip.:Pull the rope through the rotor and 
secure it with a simple overhand 
knot.
:Go to Installing the rope rotor.
Replacing a Broken Rewind 
SpringTwo types of replacement spring are 
available from the factory:
– A ready-to-fit rewind spring secured 
with a wire retainer.
– A rope rotor with pre-installed 
rewind spring.
Installing the ready-to-fit rewind 
spring
:Lubricate the spring with a few 
drops of non-resinous oil – see 
Special Accessories – do not open 
the wire retainer!
5
392BA014 KN
67
392BA015 KN
392BA024 KN 
						

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HT 70, HT 75 :Carefully remove the parts of the old 
spring from the starter cover and 
rope rotor.
:Insert the new rewind spring in the 
rope rotor and, at the same time, 
engage the outer spring loop in the 
rotor’s recess – the wire retainer 
slips off in this process. 
If the spring pops out and uncoils, 
refit it in the counterclockwise 
direction, starting outside and 
working inwards.
:Go to Installing the Rope Rotor.
Installing rope rotor with rewind 
spring
:Carefully unpack the new rope rotor 
with rewind spring. The spring may 
pop out if not handled with care –
risk of injury.
:Lubricate the spring with a few 
drops of non-resinous oil – see 
Special Accessories.
:Go to Installing the Rope Rotor.
Installing the Rope Rotor:Check dimension a for inner spring 
anchor loop and bend it slightly if 
necessary.
:Coat rope rotor bearing bore with 
non-resinous oil – see Special 
Accessories.
:Slide the rotor onto the starter post – 
turn it back and forth until the rewind 
spring anchor loop (8) engages.
:Insert the screw (5) and tighten it 
down securely.
:Go to Tensioning the Rewind 
Spring.
Tensioning the Rewind Spring:Make a loop in the unwound 
starter rope and use it to turn 
the rope rotor six full revolutions 
counterclockwise. Hold the rotor 
steady – straighten the twisted rope 
– release the rotor – 
let go of rope slowly so that it winds 
onto the rotor.
:Check spring tension:
– The starter grip must be firmly 
seated in the rope guide bush. 
If the grip droops to one side: Add 
one more turn on rope rotor to 
increase spring tension.
– When the starter rope is fully 
extended it must be possible to 
rotate the rotor another half turn. If 
this is not the case, the spring is 
overtensioned and could break. 
Take one turn of rope off the rotor.
:Go to Fitting the Starter Cover.
a
389BA029 KN
a = 2mm
(0.08 in)
8
392BA025 KN
392BA044 KN 
						

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Fitting the Starter Cover:Push the upper mounting boss 
under the shroud –
line up the tank and push the lower 
part of cover onto the tank.
:Insert and tighten down the housing 
screws.
Secure cable lug (arrow) in position 
(if fitted on your machine).For periods of about 3 months or longer:
:Drain and clean the fuel tank in a 
well ventilated area.
:Run engine until carburetor is dry, 
this helps prevent the carburetor 
diaphragms sticking together.
:Remove the saw chain and guide 
bar, clean them and spray with 
corrosion inhibiting oil.
:Thoroughly clean the machine, 
pay special attention to the cylinder 
fins and air filter.
:If you use a biological chain and bar 
lubricant, e.g. STIHL BioPlus, 
completely fill the chain oil tank.
:Store the machine in a dry and high 
or locked location, out of the reach 
of children and other unauthorized 
persons.
Replace the chain sprocket after using 
two chains!
Replace sooner if the wear marks 
on the sprocket are deeper than 
about 0,02 (0.5 mm)(dimension a) 
since this would otherwise shorten 
the life of the chain.
Use gauge – see Special 
Accessories – to check the depth of the 
wear marks.
It is best to use two chains in 
rotation with one sprocket.
Use only original STIHL chain sprockets!
410BA019 KN
Storing the Machine Checking the Chain 
Sprocket
a
390BA012 KN 
						

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HT 70, HT 75HT 70:Remove the chain sprocket cover, 
chain and guide bar.
:Use a screwdriver to remove the E-
clip (1).
:Pull the washer (2) and sprocket (3) 
off the gear shaft.
:Clean the stub of the gear shaft and 
lubricate with STIHL grease – see 
Special Accessories.
:Fit the new chain sprocket on the 
gear shaft.
:Fit the washer and E-clip on the 
gear shaft.
HT 75The chain sprocket is driven through a 
friction clutch. It may only be replaced by 
an authorized STIHL servicing dealer.
Replacing Chain SprocketHT 70
1
23
386BA014 KN 
						

							37 HT 70, HT 75english
Correctly sharpened chainA properly sharpened chain slices 
through wood effortlessly and requires 
very little feed pressure.
Do not work with a dull or damaged saw 
chain as it will increase the physical 
effort required, produce unsatisfactory 
results and a higher rate of wear.
:Clean the chain. 
:Check the chain for cracks in the 
links and damaged rivets.
:Replace any damaged or worn parts 
of the chain and match the new 
parts to the shape and size of the 
original parts by filing back as 
necessary. 
It is necessary to comply with the 
angles and dimensions specified 
below. If the saw chain is 
incorrectly sharpened – especially 
if the depth gauges are too low – 
there is an increased risk of 
kickback and resulting injury!The pruner’s saw chain cannot be 
locked in place on the guide bar. 
Therefore, it is best to remove the 
chain from the bar and resharpen it 
on a workshop sharpening tool 
(FG 2, HOS, USG).
:Select the appropriate sharpening 
tools for the chain pitch. 
See Specifications for the 
permitted chain pitches.
The chain pitch (e.g. 3/8) is marked on 
the depth gauge of each cutter.
Use only special saw chain files! 
Other files have the wrong shape and 
cut.Select the file diameter according to the 
chain pitch (se table Sharpening Tools 
at the end of this chapter).
You must also observe the following 
angles when resharpening the chain 
cutters.
A =Filing angle
B =Side plate angle
Cutter shape: Micro = Semi-chisel
Specified angles A and B are more 
readily obtained if recommended files or 
sharpening tools and correct settings 
are used.Maintaining and Sharpening 
Saw Chain
3/8
689BA020 KN
Chain type Angle (°)
AB
Picco Micro Mini (PMN) 30 85
A
B
689BA021 KN 
						

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HT 70, HT 75 Furthermore, the angles must be the 
same on all cutters. If angles are uneven 
the chain will run roughly, not in a 
straight line, wear quickly and break 
prematurely.
As these requirements can be met only 
after sufficient and constant practice:
:Use a file holder
A file holder must be used for manual 
resharpening of saw chain (see table 
Sharpening Tools). The correct filing 
angles are marked on the file holder.
For checking anglesUse a STlHL filing gauge (see table 
Sharpening Tools). This is a universal  
tool for checking the filing and side plate 
angles, depth gauge setting and cutter 
length. It also cleans the guide bar 
groove and oil inlet holes.File correctly:If you use an FG 2, HOS or USG 
sharpener: Remove the chain from 
the bar and sharpen according to 
instructions supplied with the tool.
:Sharpen chain frequently; take 
away as little metal as possible – 
two or three strokes of the file are 
usually enough.:Hold the file horizontally (at right 
angle to side of guide bar) and file 
according to the angles marked on 
the file holder. Rest the file holder on 
the top plate and depth gauge.
:Always file from the inside to the 
outside of the cutter.
:The file only sharpens on the 
forward stroke – lift the file off the 
cutter on the backstroke.
:Avoid touching the tie straps and 
drive links with the file.
689BA025 KN
90°
60°
85° 70°
80°
0° 35°
10° 30°
689BA022 KN
689BA018 KN
90°
689BA043 KN 
						

							39 HT 70, HT 75english
:Rotate the file at regular intervals 
while filing to avoid one-sided wear.
:Use a piece of hardwood to remove 
burrs from cutting edge.
:Check angles with the filing gauge.
All cutters must be the same length.
If the cutters are not the same length, 
they will have different heights. This 
makes the chain run roughly and 
increases the risk of breakage of the 
chain. 
:Find the shortest cutter and then file 
all other cutters back to the same 
length – it is best to have this work 
done in a workshop on an electric 
grinder.
Depth gauge settingThe depth gauge determines the height 
at which the cutter enters the wood and 
thus the thickness of the chip removed.
Distance between depth gauge and 
cutting edge a =  0.018(0.45 mm).
This setting may be increased by 0.008  
(0.2mm) for cutting softwood in mild 
weather season – no frost.Lowering depth gaugesThe depth gauge setting is reduced 
when the chain is sharpened because 
the top plate of the cutter slopes 
downward towards the back. 
:Check the depth gauge setting 
every time you sharpen the chain.:Place a filing gauge (1) that 
matches the chain pitch on the 
chain – if the depth gauge projects 
from the filing gauge, the depth 
gauge has to be lowered.
:File down the depth gauge until it is 
level with the filing gauge.
689BA023 KN
a
689BA047 KN
1
689BA051 KN