39
Series 4137 Components - HT
– Remove the carburetor,
:
Take out the screw (1).
:
Remove the end cover (2).
VA
936RA032
2
1
:
Remove the gasket (1).
VA
936RA033
1
:
Remove the pump diaphragm
(1).
If the gasket and pump diaphragm
are stuck together, remove and
separate them very carefully.
VA
936RA034
1
– Inspect the diaphragm and
gasket and replace if necessary.
The diaphragm is a very delicate
component. As a result of the
alternating stresses the material
eventually shows signs of fatigue,
i.e. the diaphragm distorts and
swells and has to be replaced.
:
Examine the fuel strainer (1) for
contamination and damage and
replace if necessary.
Install in the reverse sequence.
VA
936RA086
1
:
The pump diaphragm (1) and
gasket (2) are held in position by
the pegs (arrows) on the end
cover (3).
VA
932RA259
3
2
1
This carburetor has no high speed
screw (H).
The carburetor is tuned so that the
engine receives an optimum fuel-air
mixture under all operating
conditions.
Emissions at idle speed and part
load are reduced by limiting the flow
of idle mixture.
Standard setting
When adjusting from scratch, first
carry out the standard setting.
:
Carefully turn the low speed
screw (1) clockwise until it is
firmly against its seat.
VA
936RA423
L A
L
1
:
Open the low speed screw (1)
one full turn.
– Mount the bar and chain.
– Tension the chain properly.
– Check the air filter and clean or
replace as necessary.
– Adjust the throttle cable (if
adjustment is possible).
– Start the engine and allow it to
warm up.
9.3.6
Pump Diaphragm
9.4
Adjusting the Carburetor
9.4.1
Carburetor with Two
Adjusting Screws