13.4.1 Leakage Test; Servicing The Carburetor; Disassembling And Cleaning The - Stihl MS 661 Manual

13.4.1 Leakage Test

In the case of problems with the
carburetor or fuel supply system,
also check and clean or replace the
tank vent, b 13.10
On versions with M-Tronic the
switch unit / solenoid valve on the
carburetor may also be the cause of
a malfunction, b 8.3.
The carburetor can be tested for
leaks with the pump
0000 850 1300.
– Remove filter base with wiring
harness still attached and put it to
one side, b 13.3
– Remove the carburetor, b 13.4
1
: Connect fuel hose (1) from pump
0000 850 1300 to the elbow
connector (arrow).
MS 661, MS 661 C-M
2
1
: Push the ring (1) to the right and
pump air into the carburetor until
the pressure gauge (2) indicates
a pressure of about 0.8
bar (80 kPa).
If this pressure remains constant,
the carburetor is airtight. However, if
it drops, there are three possible
causes:
1. Metering diaphragm or gasket
damaged, replace as
necessary,
b 13.5.3
2. The inlet needle is not sealing
(foreign matter in valve seat,
sealing cone of inlet needle
is damaged or
inlet control lever is sticking),
remove to clean,
b 13.5.4
3. Pump diaphragm or
gasket damaged,
replace if necessary, b 13.5.5
– Test the tank vent if necessary,
b 13.10.1
– After completing the test, push
the ring (1) to the left to vent the
system and then pull the fuel
hose off the carburetor.
– Install the carburetor, b 13.4
– Reassemble all other parts in the
reverse sequence.
13.5

Servicing the Carburetor

13.5.1 Disassembling and
Cleaning the Carburetor
Cleaning the carburetor in an
ultrasonic bath is not
recommended.
The carburetor may be opened only
if its exterior is absolutely clean.
Do not allow dirt to enter the bores
or ports.
Do not store open and cleaned
carburetors for long periods
unprotected.
Perform the following steps to
remove dirt and deposits:
– Use compressed air to remove
loose dirt, then, if necessary,
clean with a brush and a standard
solvent-based degreasant
containing no chlorinated or
halogenated hydrocarbons.
– Remove the metering chamber
cover and pump cover,
diaphragm and gaskets.
– Pull off the limiter caps and
remove the low speed and high
speed screws (without M-Tronic),
inlet needle and fuel strainer.
– Do not remove the following
parts: Press-fitted or bonded
parts such as cover of idle
chamber, idle jet, part load jet,
main jet and idle speed
screw (LA).
– Only remove the choke shaft,
throttle shaft and throttle shutter if
they are stiff, clean the shaft and
bearing bore.
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