Dolmar PS-7900 - Manuel (Page 26)

26
E
Working in winter
In order to prevent carburetor icing in conditions of low tempe-
rature combined with high humidity, and below + 5°C in order
to get up to operating temperature faster, heated air can be
taken from the cylinder.
Remove the filter hood (see „Cleaning air filter“)
Remove the insert (10) and insert it as shown in position B for
cold-weather operation.
At temperatures above + 5°C the carburetor must NOT be fed
heated air. Failure to follow these instructions can lead to
damage to the cylinder and piston!
At temperatures over +5°C place the insert in position A for
normal operation.
Position A - Normal operation
Position B - Cold-weather operation
Reinstall the filter hood.
D
B A
10
L H
S
CAUTION:
Do not adjust the carburetor until the machine has been
completely assembled and checked! Do not adjust the
carburetor without a tachometer!
Carburetor adjustment is necessary for optimum engine
performance, for safer and more economical operation.
Adjust the carburetor only with the engine warm, a clean
air filter, and properly installed cutting tool.
Carburetor adjustment may be done only by a DOLMAR
service centre. Improper adjustment can cause damage
to the engine.
In order to comply with new emissions legislation, limits have
been placed on the carburetor adjusting screws (H) and (L).
This limitation (to about 180 degrees) prevents an exces-
sively rich mixture. This in turn ensures compliance with
emissions rules as well as optimum engine performance and
economical fuel consumption.
You will need a tachometer (part No. 950 233 210) for op-
timum adjustment. Exceeding the maximum permissible
speed can lead to overheating and under-lubricating, and
damage to the engine!
Factory setting of adjusting screws (H) and (L): Turned out
almost all the way (counterclockwise).
Use a screwdriver (blade width 4 mm, part No. 944 340 001)
to adjust the screws.
For proper adjustment, proceed as follows:
Checking adjusting screw (H)
Before starting the engine make sure that adjusting screw (H) is
turned out counterclockwise until it reaches a noticeable stop.
The limitations do not prevent excessively lean (under-lu-
bricated) running!
1. Start engine and let it warm up (3-5 minutes)
2. Set idle
3. Check acceleration
4. Set maximum permissible speed
5. Check idle speed
2. Set idle
Set the idle speed per the technical specifications.
Turning the adjusting screw (S) in (clockwise) increases the
idle speed. Turning it out (counter-clockwise) lowers the idle
speed. The cutting tool must not rotate!
3. Check acceleration
When the throttle is pressed, the engine should go smoothly
from idle to high speed.
Turn adjusting screw (L) out (counterclockwise) in small
increments until acceleration is good.
4. Set maximum permissible speed
Set the maximum speed by minimal adjustments of the
adjusting screw (H) in accordance with the technical
specifications. Turning the adjusting screw (H) clockwi-
se increases the speed. Never exceed the maximum
permissible speed!
For units with electronic engine speed limitation: No
tachometer is necessary to determine the maximum
permissible speed, since exceeding this speed will
result in clearly audible ignition misses!
5. Check idle speed
Check the idle speed after setting the top speed (the
cutting tool must not rotate!).
Repeat the adjustment procedure starting at Step 2,
until the engine runs with the correct idle speed, good
acceleration, and maximum permissible speed.
Adjusting the carburetor
H - +
H
S - +
S - +
L - +