Yamaha YZ125X 2023 Owner's Manual page 132

Symptom
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
• Closed to 1/4 throttle
*Hard breathing
Speed down
• Closed to 1/4 throttle
Poor acceleration
White smoke
• Unstable at low speeds
Pinking noise
Poor response at extremely
low speed
Poor response in the low to
intermediate speeds
Poor response when throt-
tle is opened quickly
Poor engine operation
* marked: In case of hard breathing, check the carburetor breather hoses for clogging.
This should be taken simply for an example. It is necessary to set the carburetor while checking the
operating conditions of the engine and discoloration of spark plugs.
Normally, carburetor setting is made by means of the main jet, jet needle clip position (including one
with 0.5 difference), pilot jet and pilot air screw. It the result of setting is still unsatisfactory, it is advisable
to change the diameter of the straight portion of the jet needle.
Setting
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)
Use jet needle having a smaller diam-
eter.
Use jet needle with a larger diameter.
Lower jet needle clip position. (1
groove down)
Turn in pilot air screw.
Reduce pilot jet calibration No.
Turn out pilot air screw.
If not effect, reverse the above proce-
dures.
Raise jet needle clip position.
If no effect, reverse the above proce-
dures.
Check overall settings.
Use main jet having lower calibration
No.
Raise jet needle clip position. (1
groove up)
If no effect, reverse the above proce-
dures.
Turn in pilot air screw.
8-7
Checking
1. Groove 1
2. Groove 2
3. Groove 3
4. Groove 4
5. Groove 5
6. Jet needle
7. Clip
The clip position is the jet needle
groove on which the clip is installed.
The positions are numbered from the
top.
It a change in the clip position (1
groove) is effective, try another jet
needle that provides a difference of
0.5 in the clip position.
Dragging brake
Overflow from carburetor
Check air filter for fouling.
Check throttle valve operation.
ENGINE
Leaner
(Standard)
Richer