engine YAMAHA YFZ50 2021 Service Manual

9-11
92. Check the spark plug for electrode erosion
and excessive carbon or other deposits, and
replace it if necessary.
3. Measure the spark plug gap with a wire thick- ness gauge and, if necessary, adjust the gap
to specification. To install the spark plug
1. Clean the surface of the spark plug gasket and its mating surface, and then wipe off any
grime from the spark plug threads.
2. Install the spark plug with the spark plug wrench, and then tighten it to the specified
torque.
TIPIf a torque wrench is not available when installing
the spark plug, a good estimate of the correct
torque is 1/4–1/2 turn past finger tight. However,
the spark plug should be tightened to the speci-
fied torque as soon as possible. 3. Install the spark plug cap.EBU37001Engine oilThe engine oil level should be checked before
each ride. In addition, the oil must be changed at
the intervals specified in the periodic maintenance
chart.
Specified spark plug:
NGK/CR6HSA
1. Spark plug gapSpark plug gap:0.6–0.7 mm (0.024–0.028 in)
Tightening torque:Spark plug:12 N·m (1.2 kgf·m, 8.9 lb·ft)
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9
To check the engine oil level
1. Park the ATV on a level surface.
2. Wait for the engine to cool.
TIPIf the engine was started before checking the oil
level, wait 10 minutes. This will allow oil to settle
into the crankcase for an accurate reading. 3. Remove the engine oil filler cap and wipe the dipstick with a clean rag.
4. Insert the dipstick into the filler hole, screw it in, and then remove it again to check the oil
level. 5. If the engine oil is at or below the minimum
level mark, add sufficient quantity of the rec-
ommended engine oil. NOTICE: Be sure the
engine oil is at the correct level, otherwise
engine damage may result.
[ECB00852]
6. Check the O-ring for damage, and then insert the dipstick and tighten the engine oil filler
cap.
To change the engine oil 1. Park the ATV on a level surface.
1. Engine oil filler cap
1
1. Engine oil filler cap
2. O-ring
3. Engine oil dipstick
4. Maximum level mark
5. Minimum level mark
14523
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92. Start the engine, warm it up for several minu-
tes, and then turn it off.
3. Place an oil pan under the engine to collect the used oil.
4. Remove the engine oil filler cap, and then re- move the engine oil drain bolt to drain the oil
from the crankcase. NOTICE: When remov-
ing the engine oil drain bolt, the compres-
sion spring, oil strainer and O-ring will fall
out. Take care not to lose these parts.
[ECB00312]
5. Clean the oil strainer with solvent.
6. Discard the old engine oil drain bolt O-ring, and then apply a thin coat of clean engine oil
to the new O-ring.
7. Install the oil strainer, the compression spring, the new O-ring and the engine oil
drain bolt. Tighten the engine oil drain bolt to
the specified torque. NOTICE: Before in-
stalling the engine oil drain bolt, be sure to
install the O-ring, compression spring and
oil strainer.
[ECB00322]
8. Refill with the specified amount of the recom- mended engine oil.
1. Oil strainer
2. Compression spring
3. O-ring
4. Engine oil drain bolt
1234
Tightening torque:Engine oil drain bolt:25 N

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9
TIPBe sure to wipe off spilled oil on any parts after the
engine and exhaust system have cooled down. NOTICEECB00331Do not use oils with a diesel specification of
“CD” or oils of a higher quality than speci-
fied. In addition, do not use oils labeled “EN-
ERGY CONSERVING II” or higher.
 Make sure that no foreign material enters the
crankcase. 9. Check the engine oil filler cap O-ring for dam-
age, and then install and tighten the engine oil
filler cap.
10. Start the engine, and then let it idle for several minutes while checking it for oil leakage. If oil
is leaking, immediately turn the engine off and
check for the cause.
11. Turn the engine off, wait at least ten minutes, and then check the oil level and correct it if
necessary.
EBU38620Why YamalubeYAMALUBE oil is a Genuine YAMAHA Part born ofthe engineers’ passion and belief that engine oil is
an important liquid engine component. We form
teams of specialists in the fields of mechanical en-
gineering, chemistry, electronics and track test-
ing, and have them develop the engine together
with the oil it will use. Yamalube oils take full ad-
vantage of the base oil’s qualities and blend in the
ideal balance of additives to make sure the final oil
clears our performance standards. Thus,
Yamalube mineral, semisynthetic and synthetic oils have their own distinct characters and value.
Yamaha’s experience gained over many years of research and development into oil since the
1960’s helps make Yamalube the best choice for
your Yamaha engine.
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91. Park the ATV on a level surface.
2. Remove the seat. (See page 5-13.)
3. Remove the air filter case cover by unhooking
the air filter case cover holders. 4. Remove the air filter element, and clean it with
solvent. WARNING! Always use parts
cleaning solvent to clean the air filter ele-
ment. Never use low-flash-point solvents
or gasoline to clean the air filter element
because the engine could catch fire or ex-
plode.
[EWB03540]
1. Air filter case check hose
1
1. Air filter case cover
2. Air filter case cover holder
1
2
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9
5. Squeeze the excess solvent out of the air filter
element and let it dry. NOTICE: Do not twist
the air filter element when squeezing it.
[ECB02310]
6. Check the air filter element and replace it if damaged.
7. Apply Yamaha foam air filter oil or other qual- ity foam air filter oil to the element.TIPThe air filter element should be wet but not drip-
ping. 8. Insert the air filter element into the air filtercase.
9. Install the air filter case cover by hooking the holders onto the air filter case. NOTICE:
Make sure that the air filter element is
properly seated in the air filter case. Never
operate the engine with the air filter ele-
1. Air filter element
1
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9-19
9ment removed. This will allow unfiltered air
to enter the engine, causing rapid engine
wear and possible engine damage. Addi-
tionally, operation without the air filter ele-
ment will affect carburetor jetting with
subsequent poor performance and possi-
ble engine overheating.
[ECB00462]
10. Install the seat.TIPThe air filter element should be cleaned every 20–
40 hours. It should be cleaned and lubricated
more often if the ATV is operated in extremely dusty areas. When servicing the air filter element,
be sure to check the air inlet of the air filter case
for obstructions.
EBU28905Cleaning the spark arresterBe sure the exhaust pipe and muffler are cool be-
fore cleaning the spark arrester.1. Tailpipe bolt
2. Tailpipe
3. Spark arrester
4. Gasket
1
2
3
4
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9
WARNING
EWB02342Always let the exhaust system cool prior to
touching exhaust components.
Do not start the engine with the spark arrester
removed. Sparks or exhaust particulate can
cause eye injury, burns, or start a fire. 1. Remove the tailpipe bolts.
2. Remove the tailpipe by pulling it out of themuffler, and then remove the gasket.
3. Tap the tailpipe lightly, and then use a wire brush to remove any carbon deposits from
the spark arrester portion of the tailpipe and
inside of the tailpipe housing.
4. Check the gasket for damage. Replace if nec- essary.
5. Install the gasket onto the tailpipe, then insert the tailpipe into the muffler and align the bolt
holes.
6. Install the bolts and tighten to the specified torque.
EBU23942Adjusting the carburetorThe carburetor should be checked and, if neces-
sary, adjusted at the intervals specified in the pe-
riodic maintenance chart. The carburetor is an
important part of the engine and requires very so-
phisticated adjustment. Therefore, most carbure-
tor adjustments should be left to a Yamaha dealer,
who has the necessary professional knowledge
and experience. The adjustment described in the
following section, however, may be performed by
the owner as part of routine maintenance.NOTICEECB00481The carburetor has been set and extensively
tested at the Yamaha factory. Changing these
settings without sufficient technical knowl-
edge may result in poor performance of or
damage to the engine. EBU24002Adjusting the engine idling speedThe engine idling speed must be checked and, if
necessary, adjusted as follows at the intervals
specified in the periodic maintenance chart.
Tightening torque:
Tailpipe bolt:10 N·m (1.0 kgf·m, 7.4 lb·ft)
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9
TIPA diagnostic tachometer is needed to make this
adjustment. 1. Start the engine and warm it up.TIPThe engine is warm when it quickly responds to
the throttle. 2. Attach the tachometer to the spark plug lead.
3. Check the engine idling speed and, if neces-sary, adjust it to specification by turning the
throttle stop screw at the carburetor. To in-
crease the engine idling speed, turn the throt-
tle stop screw in direction (a), and to decrease
it, turn the screw in direction (b).
TIPIf the specified idling speed cannot be obtained as
described above, have a Yamaha dealer make the
adjustment. 1. Throttle stop screwEngine idling speed:1600–1800 r/min
(a)
(b)
1
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9
EBU33951Adjusting the throttle lever free playPeriodically check the throttle lever free play and
adjust if necessary.TIPThe engine idling speed must be checked and ad-
justed before adjusting the throttle lever free play.
1. Slide the rubber covers apart.
2. Loosen the locknut.
3. To increase the throttle lever free play, turnthe throttle lever free play adjusting nut in di-
rection (a). To decrease the throttle lever free
play, turn the adjusting nut in direction (b).
4. Tighten the locknut.
5. Slide the rubber covers to their original posi- tions.EBU24062Valve clearanceThe valve clearance changes with use, resulting in
improper air-fuel mixture and/or engine noise. To
prevent this from occurring, the valve clearance
must be adjusted by a Yamaha dealer at the inter-
vals specified in the periodic maintenance chart.EBU29602BrakesReplacement of brake components requires pro-
fessional knowledge. Brake service should be
performed by a Yamaha dealer.
1. Rubber cover
2. Throttle lever free play adjusting nut
3. Locknut
4. Throttle lever free playThrottle lever free play:2.0–3.2 mm (0.08–0.13 in)
1
2
3
1
4
(a)(b)
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