Yamaha F4B Service Manual page 57

Symptom 2
Compression pressure
is low
Symptom 1: Unstable engine idle speed, poor acceleration, poor performance, limited engine
speed, or engine stalls.
Symptom 2
Fuel not supplied
Throttle valve does not
move properly
Spark is weak
Improper fuel and air
amount supplied
Symptom 1: High engine idle speed.
Symptom 2
Improper fuel and air
amount supplied
Symptom 1: Engine overheats.
Symptom 2
Cooling water not dis-
charged from the cooling
water pilot hole
—
Cause
Compression leakage
Improper valve timing
Cause
—
Carburetor malfunction
Throttle link and throttle cable
not installed properly
—
Choke valve does not operate
properly
Carburetor malfunction
Air leakage (carburetor to cylin-
der head)
Cause
Carburetor malfunction
Throttle link and throttle cable
not installed properly
Cause
Clogged cooling water inlet
Water pump impeller malfunc-
tion
Water leakage from the water
pump housing
Leak or clogged cooling water
passage
Thermostat malfunction
Outboard motor troubleshooting
Checking step
Measure the compression pressure.
Check the valve for bends or stuck.
Check the decompressor for proper
operation.
Check the piston and piston ring for
damage.
Check the cylinder for damage.
Check the valve timing.
Checking step
Check that the air vent screw is open.
Check the throttle valve for proper move-
ment.
Adjust the throttle link and throttle cable.
Check the CDI unit air gap.
Check the choke valve operation.
Adjust the pilot screw.
Disassemble and clean the carburetor.
Check the O-ring and gaskets of the car-
buretor and intake manifold.
Checking step
Adjust the pilot screw.
Disassemble and clean the carburetor.
Adjust the throttle link and throttle cable.
Checking step
Check the cooling water inlet.
Check the impeller.
Check the pin.
Check the insert cartridge.
Check the outer plate cartridge.
Check the water pump housing.
Check the water pipe for damage and
proper installation.
Check the cooling water passage.
Check the thermostat.
See
page
7-1
0
7-27
7-44
7-41
1
7-41
7-37
2
See
page
3
—
6-18
4
6-14
7-1
—
5
6-19
6-18
6-10
6
See
7
page
6-19
6-18
8
6-14
See
9
page
10-7
8-6
10
8-6
8-6
8-6
8-6
9-9
2-16
7-35
A
4-2