Yamaha YZ125 2009, Owner'S Service Manual

Page: 220 / 234

7-4
ENGINE
A. Difference in straight portion dia.
B. Difference in clip position
a. Reference needle
b. 0.5 richer
c. 0.5 leaner
RELATIONSHIP WITH THROTTLE OPENING
The flow of the fuel through the carburetor main
system is controlled by the main jet and then, it
is further regulated by the area between the
main nozzle and the jet needle. On the relation-
ship between the fuel flow and the throttle
opening, the fuel flow relates to the straight por-
tion of the jet needle at full closed–1/8 throttle,
to the 1st tapered portion at 1/4 throttle, to the
second tapered portion at 1/2 throttle, to the
third tapered portion at 3/4 throttle and to the
fourth tapered portion at full open.
Therefore, the fuel flow is balanced at each
stage of throttle opening by a combination of
the jet needle diameter and clip position.
<Example>
(For USA and CDN)
(For EUROPE, AUS, NZ and ZA)
A. Lean (larger diameter)
B. Rich (smaller diameter)
C. 1st taper
D. 2nd taper
E. 3rd taper
F. 4th taper
1. Full closed
2. 1/4 throttle
3. 1/2 throttle
4. 3/4 throttle
5. Full open
a. Main nozzle
6BFY43-73
6BFY43-74
6BFY43-75
6BFY44-74
6BFY43-74
6BFY42-74
6BFY42-74-3
6BFY42-74-2
6BFY42-75-3
6BFY43-74-3
6BFY43-74-2
6BFY43-75-3