Carburettor - GEISMAR STUMEC MTZ 350S Manual

5.1.4 Carburettor

On leaving our works, the carburettor has been
adjusted for optimal performance under the
weather and barometric conditions present at the
manufacturing site at the time.
Only rotate the carburettor adjustment screws in
small increments and with the utmost care, as the
slightest movement can lead to significant
changes in the way the engine runs.
Over and above normal servicing operations
during use, we recommend that any possible
carburettor repairs or adjustments be carried out
by members of the GEISMAR / STIHL sales or
repair network.
•
Standard setting :
➊ Stop the engine.
➋ Check the air filter (replace if required
see §5.1.11).
➌ Check the spark-arrester grid in the
silencer (clean or replace if required) >>
see §5.1.5.
➍ Taking the utmost care:
→ Turn the high-speed fuel-air ratio screw
Ref. H down to the stop (¾ of a turn at
the most).
→ Turn the idling-speed fuel-air ratio
screw Ref. L down to the stop and then
open it by 1 turn.
5.1
• Idling speed adjustment :
If the engine stalls at idling speed:
- Carry out the standard setting procedure as
described above.
- Turn the idling speed adjustment stop-
screw, Ref.LA, clockwise until the disc
starts rotating and then turn the screw 1
turn backwards.
If the disc rotates at idling speed:
- Carry out the standard setting procedure as
described above.
- Turn the idling speed adjustment stop-
screw, Ref. LA, anti-clockwise until the
disc stops rotating and then turn the screw
1 more turn in the same direction.
If idling speed is irregular and acceleration
unsatisfactory:
The idling speed mix is too poor (in the
event of a drop in ambient temperature).
- Turn the idling-speed fuel-air ratio screw,
Ref. L about ¼ of a turn anti-clockwise
until the engine runs smoothly and
accelerates correctly.
MTZ_Gb_00303_070525.doc
If the idling speed cannot be increased
sufficiently with adjustment screw Ref. LA, if
the engine stalls during the transition phase
between partial load and idling speed:
- Turn the idling-speed fuel-air ratio screw
Ref. L about ¼ of a turn clockwise.
• Correcting carburettor settings for use at
high altitude:
Should the engine not run satisfactorily, a
number of slight adjustments may be required.
➊ Check the standard settings.
➋ Let the engine warm up.
➌ Adjust the idling speed correctly.
➍ Turn the high-speed fuel-air ratio screw
Ref. H clockwise (for making the mix
slightly poorer).
Making the fuel-air mix too poor is liable
to damage the engine due to lack of
lubrication or overheating.
NB: All the carburettor settings can be made
with the flat-headed screwdriver provided as
standard tooling for the machine.
5.1