Yamaha YZ125(D) Owner's Service Manual page 71

HANDLING NOTE
Do not disassemble the venturi
block "1" and main nozzle "2" be-
cause it will cause a drop in carbu-
retor performance.
REMOVING THE THROTTLE
VALVE
1. Remove:
• Throttle valve "1"
• Ring "2"
• Spring (throttle valve) "3"
• Mixing chamber top "4"
• Throttle cable "5"
While compressing the spring (throt-
tle valve), disconnect the throttle ca-
ble.
CHECKING THE CARBURETOR
1. Inspect:
• Carburetor body
Contamination → Clean.
When cleaning the main air pas-
sage "a", do not blow air at the fil-
ter side because it will clog the
passage with mud or sand.
• Use a petroleum based solvent for
cleaning. Blow out all passages and
jets with compressed air.
• Never use a wire.
• When cleaning the main air pas-
sage, blow air through it while cov-
ering the nozzle with a clean rag.
CARBURETOR AND REED VALVE
2. Inspect:
• Main jet "1"
• Main jet holder "2"
• Pilot jet "3"
Contamination → Clean.
• Use a petroleum based solvent for
cleaning. Blow out all passages and
jets with compressed air.
• Never use a wire.
CHECKING THE NEEDLE VALVE
1. Inspect:
• Needle valve "1"
• Valve seat "2"
Grooved wear "a" → Replace.
Dust "b" → Clean.
Always replace the needle valve and
valve seat as a set.
CHECKING THE THROTTLE
VALVE
1. Check:
• Free movement
Stick → Repair or replace.
Insert the throttle valve "1" into the
carburetor body, and check for free
movement.
4-9
CHECKING THE JET NEEDLE
1. Inspect:
• Jet needle "1"
Bends/wear → Replace.
• Clip groove
Free play exists/wear → Replace.
• Clip position
Standard clip position:
No.3 Groove
CHECKING THE FILTER
1. Inspect:
• Filter "1"
Damage → Replace.
Inspect the filter as it is assembled to
the carburetor. Do not remove the fil-
ter except when replacing it.
MEASURING AND ADJUSTING
THE FUEL LEVEL
1. Measure:
• Fuel level "a"
Out of specification → Adjust.
Fuel level "a":
9.5–10.5 mm (0.37–0.41
in)
Above the float cham-
ber mating surface
Fuel level Measurement and ad-
justment steps:
a. Remove the drain plug.
b. Connect the fuel level gauge
adapter "2" and fuel level gauge
"1" to the float chamber.
Fuel level gauge adapter:
YM-01470/90890-01470
Fuel level gauge:
YM-1312-A/90890-
01312
c. Hold the fuel level gauge vertical-
ly next to the float chamber mat-
ing surface.