Yamaha F50 Service Manual

62Y3A114-22
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4. Push the throttle control lever 1
 to the
fully open position as shown.
5. While pushing the carburetor throttle
lever 2
 against the carburetor stopper
3
, loosen, and then tighten the adjusting
screw 5
.
Adjusting the pilot screw
1. Start the engine and warm it up for 5 min-
utes to check the stability of the engine.
Adjust the pilot screw if necessary.
2. Attach the special service tool to high-
tension cord #1 1
.
3. Turn the pilot screws 2
 in direction a
until the...

FUELFuel system
4-2362Y3A11
Synchronizing the carburetors
1. Start the engine and warm it up for 5 min-
utes to check the stability of the engine.
2. Attach the special service tool to the
high-tension cord #1 1
.
3. Remove all of the plugs 2
 and attach the
special service tool and adapters to the
carburetor assembly as shown.
NOTE:
For best results, use a vacuum gauge 3
(commercially obtainable) with four adapters
like the one shown in the illustration.
4. Adjust the idle speed to 1,000 r/min by...

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5. Measure the vacuum pressure of carbu-
retor #4.
6. Turn the throttle valve adjusting screws
5
 to adjust the vacuum pressure of car-
buretors #1, #2, and #3 to the same vac-
uum variation as carburetor #4.
7. Adjust the engine idle speed to specifica-
tion.
8. After adjusting the idle speed, rev the
engine a few times and let it idle for at
least 15 seconds to check that the vac-
uum pressures stay within 50 mm Hg
(67 m bar, 1.97 in Hg) and to check the
stability of the...

FUELFuel system
4-2562Y3A11
5. Open the throttle cam 2
 slowly, and
check that the acceleration pump stopper
3
 comes in contact with point a
.
6. Turn the adjusting screw 4
 in or out until
the specified engine speed is obtained.
7. Open and close the throttle cam a few
times, and check the engine speed at the
operation point of dash-pot again. Adjust
if necessary. 

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— MEMO — 

POWR
62Y3A11
Power unit
Troubleshooting ............................................................................................. 5-1
Special service tools ................................................................................... 5-10
Power unit ..................................................................................................... 5-13
Checking the compression pressure ....................................................... 5-25
Checking the oil pressure...

62Y3A11
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Cylinder body ............................................................................................... 5-51
Removing and installing the oil filter ........................................................ 5-55
Disassembling the cylinder body ............................................................. 5-55
Checking the piston diameter .................................................................. 5-56
Checking the cylinder bore...

POWRPower unit
5-162Y3A11
Troubleshooting5
Before troubleshooting the power unit, check that all electrical connections are tight and free from
corrosion, and that the battery is fully charged to 12 V.
Symptom: Engine does not crank.
Check the starting system.
Check the power unit.
Check that the gearshift is in the 
neutral position.
Check the neutral switch for 
continuity.
Check the engine start switch 
for continuity.
Check the engine shut-off 
switch for continuity.
Replace the engine shut-off...

62Y3A115-2
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Check the wiring harnesses for 
continuity.
Replace the wiring harnesses.
Check that the combustion 
camber is filled with engine oil 
or gasoline.
Check the starter motor.
Check operation of the starter 
motor pinion.
Remove all spark plugs, and 
then the engine.
Listen for the operation sound 
of the starter relay.
Check the power unit.
Is there conti-
nuity?
Can the oper-
ation sound 
be heard?
Does the pin-
ion rotate?
Replace the starter 
relay.
Does the 
engine 
crank?...

POWRPower unit
5-362Y3A11
Symptom: Engine cracks, but will not start.
Check the ignition system.
Check the fuel system.
Check the compression pressure of power unit.
Wet spark 
plugs?
Does the 
engine start?
Wet spark 
plugs?
Out of specifi-
cation?
Out of specifi-
cation?
Check the condition of the spark 
plugs.
Check the fuel system.
Failure in starting operation
Failure in starting operation
Check the fuel system.
Check the condition of the spark 
plugs again.
Check the compression pres-
sure of...