Yamaha YZF-R125 Service Manual: Checking the ignition spark gap
1. Check:
Ignition spark gap
Out of specification
Perform the
ignition
system troubleshooting, starting with step 5.
Refer to "TROUBLESHOOTING" on page
8-3. 
NOTE:
If the ignition spark gap is within specification, the ignition system circuit is operating normally.
a. Disconnect the spark plug cap from the spark plug.
b. Connect the ignition checker "1" as shown.
2. Spark plug cap
c. Set the main switch to "ON" and the engine
stop switch to "
".
d. Measure the ignition spark gap "a".
e. Crank the engine by pushing the start switch
" 
" and gradually increase the
spark gap until
a misfire occurs.
Checking the ignition coil
1. Check:
Primary coil resistance
Out of specification Replace.
a. Disconnect the ignition coil connectors from
the ignition coil terminals.
b. Connect the pocket tester ( × 1)
to ...
Checking the crankshaft position sensor
1. Disconnect:
Crankshaft position sensor coupler
(from the wire harness)
2. Check:
Crankshaft position sensor resistance
Out of specification Replace
the crankshaft
position senso ...
Other materials:
Checking the starter clutch
1. Check:
Starter clutch rollers "1"
Starter clutch spring caps "2"
Starter clutch springs "3"
Damage/wear Replace the starter
clutch
assembly.
2. Check:
Starter clutch idle gear
Starter clutch gear
Burrs/chips/roughness/wear Replace the
defective part(s).
3. Check:
...
Checking the water pump
1. Check:
Water pump housing cover
Water pump housing
Cracks/damage Replace.
Impeller shaft
Cracks/damage/wear Replace.
Bearing
Rough movement Replace.
Radiator outlet hose
Cracks/damage Replace.
...
Installing the generator
1. Install:
Woodruff key
Generator rotor
Washer
Generator rotor nut
NOTE:
Clean the tapered portion of the crankshaft and
the generator rotor hub.
When installing the generator rotor, make sure
the woodruff key is properly sealed in the keyway
of the crankshaft.
2. Tighte ...