# MS45 Stihl Won't Start



## edsteeler (Aug 12, 2008)

I have a Stihl hedgetrimmer. I rebuilt the carb.new spark plug,new fuel. it will not start unless I pour some fuel in the carb.Where should the adjustment screws be set? What else can I try? Thanks


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## dj722000 (Oct 29, 2008)

Check the gas cap, sometimes the duck bill check valve (Little black rubber piece) in there can get plugged and keep gas from flowing. A new cap is pretty cheap. To check it, just put it on one or so turns, enough so it can get air and without fuel spilling all over. I had one of these and that was the problem. If not, try 1-1/2 turns out on the main jet.


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## edsteeler (Aug 12, 2008)

Thank You ,I will try that


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## rotti1968 (Apr 26, 2009)

base stihl settings are 1 turn each on the high and low speed screws. when it does run with the gas in the carb how long does it stay running ? how does the compression feel , will it pop you thumb off of the spark plug hole with the plug removed ? You rebuilt the carb is the needle valve working and set to the proper level so the needle opens and closes correctly?Does this carb have a single screw or 2 screws? single ld screw carb :
The carburetor with idle speed
screw (LD) has no adjusting screws
for maximum engine speed (H
screw) or idle mixture (L screw).
The carburetor is set at the factory
to provide an optimum fuel-air
mixture in all operating conditions.
Standard setting
To adjust the carburetor from
scratch, first carry out the standard
setting.
: Carefully screw the idle speed
screw (LD) counterclockwise
against its seat (left-hand thread).
: Then turn the idle speed screw
(LD) two full turns clockwise.
– Check the air filter and replace if
necessary, 
– Check the spark arresting screen
and clean or replace if necessary,

Adjusting engine idle speed
– Carry out standard setting.
– Start the engine and allow it to
warm up.
Engine stops while idling:
: Turn the idle speed screw (LD)
slowly clockwise until the engine
runs smoothly.
Erratic idling behavior, poor
acceleration:
: Turn the idle speed screw (LD)
slowly counterclockwise (no
more than 1/2 turn).
2 screws with limiter caps:
Standard setting
Do not remove the limiter cap from
the high speed screw (H) to carry
out the standard setting.
With this carburetor it is only
possible to correct the setting of the
high speed screw (H) within fine
limits
– Check the air filter and replace it
if necessary, 
– Check spark arrestor and clean
or replace as necessary,
Then make the following
adjustments:
: Turn the high speed screw (H)
counterclockwise as far as stop
(no more than 3/4 turn).
: Carefully screw the low speed
screw (L) clockwise down onto its
seat, then turn it one full turn
counterclockwise.
– Start the engine and allow it to
warm up.
: Use the idle speed screw (LA) to
adjust idle so that the cutting tool
does not move.
Fine tuning
A minor correction may be
necessary if engine power is not
satisfactory when operating at high
altitude or at sea level. Note that
even very slight corrections to the
high speed screw (H) produce a
noticeable change in engine
running behavior.
– Carry out the standard setting.
– Start the engine and allow it to
warm up.
– Open the throttle wide.
– At high altitude (mountains): Turn
the high speed screw (H)
clockwise (leaner), but no further
than stop, until there is no
noticeable increase in engine
speed.
– At sea level: Turn the high speed
screw (H) counterclockwise
(richer), but no further than stop,
until there is no noticeable
increase in engine speed.
It is possible that the standard
setting produces the highest engine
rpm in both the above cases.
Adjusting engine idle speed
– Open the low speed screw (L)
one full turn.
– Warm up the engine.
Engine stops while idling
– Turn the idle speed screw LA
slowly clockwise until the engine
runs smoothly.
Erratic idling behavior, poor
acceleration
– Idle setting is too lean. Turn the
low speed screw (L) counterclockwise
(about a quarter turn)
until the engine runs and
accelerates smoothly.


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