2001 YAMAHA TTR90 engine

3 - 7
INSP
ADJ

PILOT AIR SCREW ADJUSTMENT
5. Install:
l
Gasket
l
Drain bolt
New
T R..20 Nm (2.0 m · kg, 14 ft · lb)

6. Fill:
l
Crankcase
Oil quantity:
Periodic oil change:
0.8 L (0.70 Imp qt, 0.85 US qt)
7. Install:
l
Dipstick
8. Inspect:
l
Engine (for oil leaks)
l
Oil level
Refer to “ENGINE OIL LEVEL INSPEC-
TION”.
PILOT AIR SCREW ADJUSTMENT
1. Adjust:
l
Pilot air screw
1

Adjusting steps:
l
Screw in the pilot air screw until it is lightly
seated.
l
Back out by the specified number of turns.
Pilot air screw:
1-3/4 turns out

3 - 8
INSP
ADJ

IDLE SPEED ADJUSTMENT/
VALVE CLEARANCE ADJUSTMENT
IDLE SPEED ADJUSTMENT
1. Start the engine and thoroughly warm it
up.
2. Attach:
l
Inductive tachometer
To spark plug lead.
3. Adjust:
l
Idle speed
VALVE CLEARANCE ADJUSTMENT
NOTE:

l
The valve clearance should be adjusted
when the engine is cool to the touch.
l
The piston must be at Top Dead Center
(T.D.C.) on compression stroke to check or
adjust the valve clearance.
1. Remove:
l
Air scoop (right)
1

l
Air filter case
2
2. Remove:
lSpark plug
lTappet cover (intake side) 1
lTappet cover (exhaust side) 2 Adjustment steps:
lAdjust the pilot screw.
Refer to “PILOT AIR SCREW ADJUST-
MENT” section.
lTurn the throttle stop screw 1 until the
engine runs at the lowest possible speed.
To increase idle speed ®
Turn the throttle stop screw 1 in a.
To decrease idle speed ®
Turn the throttle stop screw 1 out b.
Inductive tachometer:
YU-8036-B/90890-03113
Engine idling speed:
1,400 ~ 1,600 r/min
3. Remove:
lTiming plug 1
lCrankshaft end cover 2
lO-rings

3 - 10
INSP
ADJ
SPARK ARRESTER CLEANING (For USA)
6. Install:
lTappet cover (intake side) 1
lO-ring 2
7. Install:
lTappet cover (exhaust side)
lO-ring
lSpark plug
lTiming plug
lCrankshaft end cover
8. Install:
lAir filter case
lAir scoop (right)
T R..18 Nm (1.8 m · kg, 13 ft · lb)
New
T R..18 Nm (1.8 m · kg, 13 ft · lb)
New
T R..13 Nm (1.3 m · kg, 9.4 ft · lb)
T R..7 Nm (0.7 m · kg, 5.1 ft · lb)
T R..7 Nm (0.7 m · kg, 5.1 ft · lb)
SPARK ARRESTER CLEANING (For USA)
WARNING
lBe sure the exhaust pipe and muffler are
cool before cleaning the spark arrester.
lDo not start the engine when cleaning the
exhaust system.
1. Remove:
lBolt (tailpipe) 1
2. Remove:
lTailpipe 2
Pull the tailpipe out of the muffler.
3. Clean:
lSpark arrester
Use a wire brush to remove any carbon
deposits from the spark arrester portion
of the tailpipe.
Tap the tailpipe lightly and remove the
carbon deposits from the outside por-
tion of the tailpipe.
4. Install:
lTailpipe
Insert the tailpipe into the muffler and
align the bolt hole.
lBolt (tailpipe)
2
1
T R..7 Nm (0.7 m · kg, 5.1 ft · lb)

3 - 12
INSP
ADJ
DRIVE CHAIN SLACK ADJUSTMENT
DRIVE CHAIN SLACK ADJUSTMENT
1. Elevate the rear wheel by placing the
suitable stand under the engine.
2. Check:
lDrive chain slack a
In the center between the drive axle
and rear wheel axle.
Out of specification ® Adjust.
NOTE:
Before checking and/or adjusting, rotate the
rear wheel through several revolutions and
check the slack several times to find the tight-
est point. Check and/or adjust chain slack with
rear wheel in this “tight chain” position.
Drive chain slack:
40 ~ 53 mm (1.6 ~ 2.1 in)
3. Adjust:
lDrive chain slack
Drive chain slack adjustment steps:
lLoosen the wheel axle nut 1.
lAdjust chain slack by turning the adjusters
2.
To tighten ®Turn adjuster 2 clockwise.
To loosen ®Turn adjuster 2 counter-
clockwise and push wheel
forward.
lTurn each adjuster exactly the same
amount to maintain correct axle alignment.
(There are marks a on each side of chain
puller alignment.)
12 a
NOTE:
Turn the adjuster so that the chain is in line
with the sprocket, as viewed from the rear.
CAUTION:
Too small chain slack will overload the
engine and other vital parts; keep the
slack within the specified limits.

3 - 13
INSP
ADJFRONT FORK INSPECTION/REAR SHOCK ABSORBER INSPECTION/
REAR SHOCK ABSORBER SPRING PRELOAD ADJUSTMENT
lTighten the wheel axle nut while pushing
down the drive chain.
T R..
Axle nut:
60 Nm (6.0 m • kg, 43 ft • lb)
EC36C000
FRONT FORK INSPECTION
1. Inspect:
lFront fork smooth action
Operate the front brake and stroke the
front fork.
Unsmooth action/oil leakage ® Repair
or replace.
EC36K000
REAR SHOCK ABSORBER INSPECTION
1. Inspect:
lSwingarm smooth action
Abnormal noise/unsmooth action ®
Grease the pivoting points or repair the
pivoting points.
Damage/oil leakage ® Replace.
REAR SHOCK ABSORBER SPRING
PRELOAD ADJUSTMENT
1. Elevate the rear wheel by placing the
suitable stand under the engine.
2. Remove:
lRear shock absorber
Refer to “SWINGARM” section in the
CHAPTER 5.
3. Remove:
lSpring guide 1
NOTE:
While compressing the spring, remove the
spring guide.

3 - 15
INSP
ADJSPOKES INSPECTION AND TIGHTENING/WHEEL INSPECTION/
STEERING HEAD INSPECTION AND ADJUSTMENT
SPOKES INSPECTION AND TIGHTENING
1. Inspect:
lSpokes 1
Bend/damage ® Replace.
Loose spoke ® Retighten.
2. Tighten:
lSpokes
NOTE:
Be sure to retighten these spokes before and
after break-in. After a practice or a race check
spokes for looseness.
T R..2 Nm (0.2 m · kg, 1.4 ft · lb)
EC36T000
WHEEL INSPECTION
1. Inspect:
lWheel runout
Elevate the wheel and turn it.
Abnormal runout ® Replace.
2. Inspect:
lBearing free play
Exist play ® Replace.
STEERING HEAD INSPECTION AND
ADJUSTMENT
1. Elevate the front wheel by placing a suit-
able stand under the engine.
2. Check:
lSteering shaft
Grasp the bottom of the forks and gen-
tly rock the fork assembly back and
forth.
Free play ® Adjust steering head.

3 - 19
INSP
ADJ
ELECTRICAL/SPARK PLUG INSPECTION
EC370000
ELECTRICAL
EC371001
SPARK PLUG INSPECTION
1. Remove:
lSpark plug
2. Inspect:
lElectrode 1
Wear/damage ® Replace.
lInsulator color 2
Normal condition is a medium to light
tan color.
Distinctly different color ® Check the
engine condition.
NOTE:
When the engine runs for many hours at low
speeds, the spark plug insulator will become
sooty, even if the engine and carburetor are in
good operating condition.
3. Measure:
lPlug gap a
Use a wire gauge or thickness gauge.
Out of specification ® Regap.
4. Clean the plug with a spark plug cleaner
if necessary.
Spark plug gap:
0.6 ~ 0.7 mm (0.02 ~ 0.03 in)
Standard spark plug:
CR6HSA (NGK)
U20FSR-U (DENSO)
5. Tighten:
lSpark plug
NOTE:
lBefore installing a spark plug, clean the gas-
ket surface and plug surface.
lFinger-tighten a the spark plug before
torquing to specification b.
T R..13 Nm (1.3 m · kg, 9.4 ft · lb)

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