SERVICE INFORMATION
SRM-420ES
8
2-3 Adjusting carburettor
SRM-420ES(L): Remove shield and cut trimmer
head line lengths to 190 mm.
SRM-420ES(U) : Remove shield and blade, and
cut trimmer head line lengths to 190 mm.
1. Start and warm engine for 3 minute alternating
engine speed between WOT for 50 seconds and
idle for 10 seconds.
2. Adjust L mixture needle (B) to reach maximum
idle speed using 2.5 mm blade screwdriver.
3. Set Idle speed to 3,550 r/min by turning Idle
adjust screw (D). Engine speed should be stable at
3,550 +/- 50 r/min.
4. Turn L mixture needle (B) anticlockwise to re-
duce engine idle speed 800 r/min to set idle speed
at 2,750 r/min. The idle speed range is 2,650 - 2,850
r/min.
5. Turn Idle adjust screw (D) clockwise to increase
idle engine speed to set idle at 2,800 r/min. The
idle speed range is 2,700 to 2,900 r/min.
NOTE :
Engine speed must be allowed to stabilize
a minimum of 20 seconds after each adjustment of
idle mixture needle to assure accurate tachometer
readings.
6. Adjust H mixture needle (C) to reach maximum
WOT engine speed. Then turn H mixture needle (C)
anticlockwise to reduce WOT engine speed 120
r/min (RANG : 100-140 r/min).
max. approx. 9,000 r/min
NOTE :
Nylon line length should be 190 mm with-
out shield.
7. SRM-420ES(L) : Stop engine, and restart en-
gine and verify engine idle speed ranges from 2,400
to 3,200 r/min, and expand and cut nylon line by
shield knife and WOT engine speed ranges from
9,500 to 10,500 r/min.
NOTE :
Nylon line length should be 150 mm with
shield
SRM-420ES(U) : Stop engine and reinstall shield
for 3-tooth blade (255 mm) and the blade. Restart
engine and verify engine idle speed ranges from
2,400 to 3,200 r/min, and WOT engine speed
ranges from 10,500 to 11,500 r/min.
Make sure the nylon line cutter does not rotate
when engine is at idle. Engine should start and ac-
celerate smoothly.
NOTE :
WOT, and idle speed in field operation
may vary from
fi
nal adjustment speci
fi
cations due
to changing ambient conditions, fuel, and engine
loads. Safe engine speed variances should be
within the WOT and Idle speed ranges listed in
Section 1-2, otherwise the carburettor should be
readjusted.
(C)
(B)
(D)
t = 190 mm
