Yamaha F2 5 Service Manual

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Features and benefits1
Ignition system
A simple and compact ignition system is adopted. In this ignition system, high voltage is induced in
the secondary coil when the electric current produced by the primary coil and the permanent mag-
net on the rotating flywheel is cut off.
This TCI (Transistor Controlled Ignition) system greatly contributes to a compact and lightweight
engine.
1TCI unit
2Permanent magnet3Flywheel
aAir gap: 0.4–0.6 mm (0.016–0.024 in)
1Flywheel
2Permanent magnet
3Core
4Primary coil
5Secondary coil6Spark plug
7Transistor 1
8Transistor 2
9Engine shut-off switch
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Identification / Features and benefits 
						

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INFO
General information
1-769M3E11
Blowby gas reburning system
The splash lubrication system splashes a large quantity of oil into the blowby gases. Therefore, a
reburning system is incorporated to separate the oil from the blowby gases in two stages: first in the
cylinder head and second in the intake silencer.
Oil is first separated from the blowby gases in the cylinder head labyrinth. The oil flows into the cyl-
inder head and the gases are discharged into the intake silencer.
Blowby gases from the cylinder head flow into the intake silencer and oil is then separated from the
gases in the intake silencer labyrinth. The oil flows from the bottom of the intake silencer into the oil
pan through the blowby hose and the gases are drawn into the carburetor and reburned in the
engine.
1To intake silencer
2From cylinder head
3To oil panÈBlowby gas
ÉEngine oil
ÊCylinder head
ËIntake silencer
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Oil check window
The F2.5 is equipped with an oil check window to make engine oil level checks easier.
The oil checking plate in the oil check window indicates the proper oil level when the outboard motor
is in an upright position.
The end of the oil checking plate indicates the minimum level. The oil level should be between the
maximum and minimum levels. 
1Oil checking plate
aMaximum level
bMinimum level
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Features and benefits 
						

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INFO
General information
1-969M3E11
Idle silencer
The idle silencer is installed to the upper case to reduce exhaust noise and carbon deposits around
the exhaust idle port.
Exhaust gases are discharged into the idle silencer from the two upper holes in the upper case. The
gases flow and eddy (swirl) inside the silencer and then are discharged from the exhaust idle port of
the silencer into the atmosphere.
The cooling water in the silencer flows into lower hole in the upper case.
ÈExhaust gas
ÉCooling water
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Splash lubrication system
A simple splash lubrication system design is adopted.
The splasher is driven by the oil splasher gear installed on the camshaft and splashes oil in the oil
pan onto the internal parts of the crankcase.
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Features and benefits 
						

							GEN 
INFO
General information
1-1169M3E11
Low vibration tiller handle
The tiller handle is installed near the center of the outboard motor for low vibration.
To help reduce vibration transferring to the tiller handle, a rubber damper is used at the installation
point of the handle.
The tiller handle is equipped with a throttle indicator to indicate the throttle angle, an engine shut-off
switch to turn the engine off in an emergency, and a throttle friction adjuster to adjust the friction of
the throttle lever.
1Rubber damper
2Throttle grip
3Throttle indicator
4Engine shut-off switch
5Throttle friction adjuster
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Technical tips1
TCI system
The TCI system operates as follows.
Before ignition
As the flywheel rotates, the primary coil generates a voltage and an electric current A
. This electric
current opens transistor Q1 and, as a result, an electric current B
 flows to the primary coil.
Ignition
As the flywheel continues to rotate, the voltage generated by the primary coil increases.
When the voltage reaches the operation voltage of transistor Q2, an electric current C
 flows to tran-
sistor Q2 and opens it. As a result, electric current D
 flows.
Ignition timing occurs in this instant.
At ignition timing, the electric current B
 flowing to the primary coil through transistor Q1 is cut off,
the secondary coil generates a high voltage by electric induction and an ignition spark is fired by the
spark plug.
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Q1
Q2
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Q2
B
Q1
Features and benefits / Technical tips 
						

							GEN 
INFO
General information
1-1369M3E11
Automatic tilt support and steering pivot immobilization system
The tilt support lever is constantly pushed against the clamp bracket by the force of a spring.
When the outboard motor is fully tilted up in the forward steering position, the stopper linked to the
tilt support lever is inserted into the swivel cutout. At the same time, the tilt support lever automati-
cally supports the outboard motor on the clamp bracket.
If the outboard motor is tilted up with the steering in either direction, the stopper is not inserted into
the swivel cutout and the tilt support lever linked to the stopper does not support the outboard
motor.
The stopper, which is fitted on the swivel, prevents the outboard motor from swiveling when fully
tilted up in the forward steering position.
1Spring
2Tilt support lever
3Stopper
4Swivel recess
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Cooling water flow chart
ÈCold water
ÉHot water
ÊExhaust gas and water
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Upper case
(Top starboard
side)Upper case
(Inside)
Crankcase
Cooling water
pilot hole
AtmosphereWater pumpLower case
exhaust port
Cooling water
inletAtmosphere
Cylinder
blockCylinder
head
Thermostat
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Technical tips 
						

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INFO
General information
1-1569M3E11
Propeller selection1
The performance of a boat and outboard
motor will be critically affected by the size
and type of propeller you choose. Propellers
greatly affect boat speed, acceleration,
engine life, fuel economy, and even boating
and steering capabilities. An incorrect choice
could adversely affect performance and
could also seriously damage the engine.
Use the following information as a guide for
selecting a propeller that meets the operating
conditions of the boat and the outboard
motor.
Propeller size
The size of the propeller is indicated on the
propeller blade.
aPropeller diameter (in inches)
bPropeller pitch (in inches)
cPropeller type (propeller mark)
Selection
When the engine speed is at the full throttle
operating range (5,250–5,750 r/min), the
ideal propeller for the boat is one that pro-
vides maximum performance in relation to
boat speed and fuel consumption.
Predelivery checks1
To make the delivery process smooth and
efficient, the predelivery checks should be
completed as explained below.
Checking the fuel system 
1. Check that the fuel hose is securely con-
nected and that the fuel tank is full with
fuel.
CAUTION:
This is a 4-stroke engine. Never use pre-
mixed fuel.
Checking the gear oil
1. Check the gear oil level.
Propeller size (in) Material
7 1/4 ×
 6 - BS
Aluminum 7 1/4 ×
 5 1/2 - BS
7 1/4 ×
 7 1/4 - BS
7 1/4 ×
 8 1/4 - BS
7 1/2 ×
 5 1/2 - BS
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abc
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