Yamaha YBR125 Custom, Service Manual, Page: 88 / 218

ENG
Check and repair
Air valve seat
1.Clean:
Carbon deposit
(Clean from working face of air valve and air valve seat)
Check:
Air valve seat
Corrosive pitting or wear → Repair the air valve surface
2.
Measure:
Width of air valve seat a
3.
Exceeding specification both are usable value range
→ Repairing air valve seat
Width of air valve seat:
Intake:
0.9 1.1 mm
Exhaust:
0.9 1.1 mm
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Meauring procedures:
1.
2.
3.
4.
5.
Paint blue dykem on working face b of air valve
Fit the air valve into cylinder cover.
Push and press the air valve to air valve seat through
guide pipe of air valve,thus to get clear trace.
Measure the width of this mark which is width of air
valve seat.No matter wherever the air valve seat contacts
working face of air valve,blue colour will never disappear.
If the air valve seat is too wide, too narrow or not in the
middle,it must be repaired.
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