Jet Needle Adjustment; Jet Needle Groove Position Adjustment - Yamaha YZ125X 2023 Owner's Manual

EAM30597

JET NEEDLE ADJUSTMENT

On the carburetors used in the YZ125X the main
nozzle is a non disassembly type, so it can not
be replaced. Therefore, carburetor setting re-
quires the change of the jet needle.
1. The jet needle setting parts, having the same
taper angle, are available in different straight
portion diameters and in different taper start-
ing positions.
Standard jet needle
* For AUS/NZL
NYCD
NYCE
NYCF
NYCG
NYCH
A. Difference in straight portion diameter
B. Difference in taper starting position
a. Diameter of the straight portion
b. Taper starting position
c. Rich
d. Lean
NYCF
*NYEE
NYFF
NYCF
NYDF
NYEF
8-3
2. Effects of changing the jet needle (reference)
• Diameter of straight portion
Changing the diameter of the straight portion
adjusts the air-fuel mixture when the throttle
is 1/8 to 1/4 open.
• Taper starting position
Changing the taper starting position produc-
es the same effect as changing the clip posi-
tion by 0.5 groove.
Example:
In case of being 0.5 groove leaner in relation
to NYCF-2nd groove, choose NYDF-2nd
groove.
A. In case of being 0.5 groove leaner in relation
to NYCF-2nd groove.
a. Difference of 0.5 groove
EAM30598
JET NEEDLE GROOVE POSITION
ADJUSTMENT
Should the engine be hard to run smoothly at in-
termediate speeds, the jet needle "1" must be
adjusted. If the mixture is too rich or too lean at
intermediate speed operation, irregular engine
operation and poor acceleration will result.
Whether or not the richness of the mixture is
proper is hard to be determined by means of the
spark plug and therefore, it should be judged
from your feeling of actual engine operation.
Standard clip position
1. Too rich at intermediate speeds
Rough engine operation is felt and the engine
will not pick up speed smoothly.
In this case, step up the jet needle clip by one
groove and move down the needle to lean out
the mixture.
2. Too lean at intermediate speeds
The engine breathes hard and will not pick up
speed quickly.
In this case, step down the jet needle clip by
one groove and move up the needle to enrich
the mixture.
ENGINE
No. 2 groove