Yamaha YZ Serie Fahrer- Und Wartungshandbuch Seite 518

EC71C020
Road condition and examples of carburetor setting
Conditions
Under 10°C
(50°F)
Parts (Winter)
#470
Main jet
*#460
6BGK10-75-3
Jet needle
*6BHY25-75-3 *6BHY1-75-3
#25
Pilot jet
*#30
1
Pilot air screw
*1-1/4
*For EUROPE
EC71D040
Examples of carburetor setting depending on symptom
Symptom
At full throttle
Stall at high speeds
*Hard breathing
Shearing noise
Whitish spark plug
Lean mixture
At full-throttle
Stop of speed pick-up
Slow speed pick-up
Slow response
Sooty spark plug
Rich mixture
Lean mixture
Rich mixture
1/4~3/4 throttle
*Hard breathing
Lack of speed
1/4~1/2 throttle
Slow speed pick-up
White smoke
Poor acceleration
General condition
15~25°C Over 30°C
(59~77°F) (86°F)
(Spring, Autumn) (Summer)
#460 #450
*#450 *#440
6BGK9-75-3 6BGK9-75-3
*6BHY1-75-3
#25 #25
*#30 *#30
1-1/4 1-1/2
*1-1/2 *1-3/4
Setting
Increase main jet calibration No.
(Gradually)
Decrease main jet calibration No.
(Gradually)
*In case of racing slight enrichment
of mixture reduces engine trouble.
Lower jet needle clip position.
(1 groove down)
Raise jet needle clip position.
(1 groove up)
Lower jet needle clip position.
(1 groove down)
Raise jet needle clip position.
(1 groove up)
7-10
TUN
SETTING
Sandy condition
Under 10°C 15~25°C
(50°F) (59~77°F)
(Winter) (Spring, Autumn)
#490 #480
*#470 *#460
6BGK9-75-4 6BGK10-75-3 6BGK10-75-3
*6BHY1-75-4 *6BHY25-75-3 *6BHY25-75-3
#25 #25
*#30 *#30
1 1-1/4
*1-1/4 *1-1/2
Checking
Discoloration of spark plug
If tan color, it is in good condition.
If can not be normalized:
Clogged float valve seat
Clogged fuel hose
Clogged fuel cock
Discoloration of spark plug
If tan color, it is in good condition.
If not effect:
Clogged air cleaner
Fuel overflow from carburetor
Clogged main air passage or clogged
filter
Clip position indicates the position of jet
needle groove, to which the clip is fitted.
The position is numbered from the top.
If a change in the clip position (1
groove) is effective, try another jet nee-
dle that provides a difference of 0.5 in
the clip position.
Over 30°C
(86°F)
(Summer)
#470
*#450
#25
*#30
1-1/2
*1-3/4
Leaner
(Standard)
Richer