Yamaha F150B, Service Manual

Page: 214 / 458

7-1
Power unit
POWR
Power unit (check and
adjustment)
Checking the compression pressure
1. Start the engine and warm up until the
engine idle speed is stable at 650–750 r/
min, and then turn it off.
2. Remove the clip from the engine shut-off
switch.
3. Disconnect all fuel injector couplers.
4. Remove the spark plug wire cover and all
spark plugs, and then install the special
service tools
a
and
b
into a spark plug
hole. NOTICE: Before removing the
spark plugs, blow compressed air in
the spark plug well to clear out any
dirt or dust that may fall into the
cylinder.
5. Disconnect the throttle cable joint from
the accelerator lever
c
, and then place
and hold the lever in the fully open
position of the throttle.
6. Crank the engine until the reading on the
compression gauge stabilizes, and then
measure the compression pressure.
7. If the compression pressure is below
specification and the compression
pressure for each cylinder is unbalanced,
add a small amount of engine oil to the
cylinder, and then measure the
compression pressure again.
TIP:
• If the compression pressure increases,
check the pistons and piston rings. Replace
if worn. See “Assembling the cylinder block”
(7-61).
• If the compression pressure does not
increase, check the valve clearances,
valves, valve seats, cylinder head gasket,
and cylinder head. Adjust or replace if nec-
essary. See “Cylinder head” (7-36).
Compression gauge
a
:
90890-03160
Compression gauge extension
b
:
90890-06563
b
a
Minimum compression pressure
(reference data):
880.0 kPa (8.80 kgf/cm
2
, 127.6 psi)
c