2003 YAMAHA TTR90 fuel

4 - 1
ENG

ENGINE
CARBURETOR
Extent of removal:
1
Carburetor removal
Extent of removal Order Part name Q’ty Remarks
CARBURETOR REMOVAL
Preparation for removal Fuel tank
1 Clamp (air filter joint) 1 Loosen the screw (air filter joint).
2 Carburetor heater lead 1
3 Air vent hose 1
4 Fuel hose 1
5 Bolt 2
6 Carburetor assembly 1
7 O-ring 1
8 Spacer 1
9 Carburetor top 1
10 Starter plunger assembly 1
1

CARBURETOR

4 - 6
ENGCARBURETOR
EC464600
Float
1. Inspect:
Float 1
Damage → Replace.
ASSEMBLY AND INSTALLATION
Carburetor
1. Install:
Pilot air screw 1
Note the following installation points:
Screw in the pilot air screw until it is lightly
seated.
Back out it by the specified number of
turns.
Pilot air screw:
1-3/4 turns out
2. Install:
Throttle valve 1
Starter plunger 2
NOTE:
Align the slit a of the throttle valve with the tab
b of the carburetor top.
FUEL LEVEL ADJUSTMENT
WARNING
Gasoline (fuel) and its vapors are highly
flammable and explosive. Keep away from
sparks, cigarettes, flames or other sources
of ignition.

4 - 7
ENGCARBURETOR
1. Measure:
Fuel level a
Use a fuel level gauge 1.
Out of specification → Adjust.
Fuel level gauge:
YM-1312-A/90890-01312
Fuel level:
2 ~ 3 mm (0.08 ~ 0.12 in) below
the float chamber line

4 - 8
ENGCYLINDER HEAD
CYLINDER HEAD
Extent of removal:1 Cylinder head removal
Extent of removal Order Part name Q’ty Remarks
CYLINDER HEAD REMOVAL
Preparation for removal Seat, fuel tank and rear fender
Exhaust pipe
Carburetor Refer to “CARBURETOR” section.
Air filter case and starter lever
1 Plug cap/spark plug 1/1
2 Crankshaft end cover/O-ring 1/1
3 Timing plug/O-ring 1/1
4 Camshaft sprocket cover/O-ring 1/1
5 Tappet cover (intake)/O-ring 1/1
6 Tappet cover (exhaust)/O-ring 1/1
7 Camshaft sprocket bolt/washer 1/1
Refer to “REMOVAL POINTS”. 8 Timing chain tensioner 1
9 Gasket 1
1

4 - 39
ENGCDI MAGNETO
CDI MAGNETO
Extent of removal:1 Pickup coil/stator assembly removal2 Rotor removal
Extent of removal Order Part name Q’ty Remarks
CDI MAGNETO AND STATOR
REMOVAL
Preparation for removal Fuel tank
Crankcase cover (left) Refer to “CLUTCH” section.
1 CDI magneto coupler 1
2 Pickup coil/stator assembly 1
3 Rotor nut 1
Use special tool.
Refer to “REMOVAL POINTS”. 4 Rotor 1
5 Woodruff key 1
1
2

4 - 41
ENGCRANKCASE AND CRANKSHAFT
CRANKCASE AND CRANKSHAFT
Extent of removal Order Part name Q’ty Remarks
CRANKCASE SEPARATION
AND CRANKSHAFT REMOVAL
Preparation for removal Seat, fuel tank and rear fender
Exhaust pipe
Air filter case
Carburetor Refer to “CARBURETOR” section.
Drain the engine oil Refer to “ENGINE OIL REPLACEMENT”
section in the CHAPTER 3.
Engine guard and drive sprocket
Engine assembly From the chassis.
Cylinder head Refer to “CYLINDER HEAD” section.
Cylinder and piston Refer to “CYLINDER AND PISTON” sec-
tion.
Clutch housing and clutch carrier Refer to “CLUTCH” section.
Kick axle assembly Refer to “KICK AXLE” section.

–+ELEC
6 - 2
IGNITION SYSTEM
EC620000
IGNITION SYSTEM
INSPECTION STEPS
Use the following steps for checking the possibility of the malfunctioning engine being attributable to
ignition system failure and for checking the spark plug which will not spark.
NOTE:
Remove the following parts before inspection.
1) Seat
2) Fuel tank
Use the following special tools in this inspection.
Spark gap testClean or replace
spark plug.
Check entire ignition
system for connection.Repair or replace.
Check “ENGINE STOP”
switch.Replace.
Check ignition coil. Primary coil Replace.
Secondary coil Replace.
Check CDI magneto. Pickup coil Replace.
Source coil Replace.
Replace CDI unit.
Dynamic spark tester:
YM-34487
Ignition checker:
90890-06754Pocket tester:
YU-3112-C/90890-03112
No Spark
OK
OK
OK
OK
Spark
No good
No good
No good
No good
No good
No good

–+ELEC
6 - 6
CARBURETOR HEATING SYSTEM
CARBURETOR HEATING SYSTEM
INSPECTION STEPS
Use the following steps for checking the possibility of the malfunctioning carburetor heating system.
NOTE:
Remove the following parts before inspection.
1) Seat
2) Fuel tank
Use the following special tools in this inspection.
Check entire carburetor
heating system for connec-
tion.Repair or replace.
Check thermo switch. Replace.
Check carburetor heater. Replace.
Check CDI magneto. Source coil Replace.
Replace rectifier/regulator.
Pocket tester:
YU-3112-C/90890-03112
OK
OK
OK
No good
No good
No good
No good
OK