Advertisement
14-2
FUEL SYSTEM DIAGNOSIS
come enlarged, making the mixture too rich for
proper performance.
AUTOMATIC CHOKE-WELL TYPE
To function properly, it
is
important that all parts
be clean and move freely. Other than an occasional
cleaning, the choke requires no servicing. However,
it
is very important that the choke control unit work
freely in the well and at the choke shaft. Move the
choke rod up and down to check for free movement
in the pivot. If the unit binds, a new choke unit should
be installed.
The well type choke is serviced as an
assembly.
Do
not attempt to repair or change the set-
ting, unless authorized by service literature. Changes
of the choke materially affect summer temperature
cold starting and seldom are a satisfactory correction
of driveability problems, which are generally associ-
ated with carburetors or vacuum diaphragms.
When installing the well type choke unit, be cer-
tain that the coil housing does not contact the sides
of the well in the exhaust manifold. Any contact at
this point will affect choke operation. DO NOT lubri-
cate any parts of the choke or the control unit. This
causes an accumulation of dirt which will result in
binding of the mechanism.
CLOSED CRANKCASE VENT SYSTEM
The closed crankcase ventilator valve is located in
the crankcase vent tube cap and is connected to the
carburetor throttle body via a rubber tube.
The function of the valve is to regulate the flow of
unburned hydrocarbons from the crankcase and re-
turn them to the intake manifold. From here they
enter the combustion chamber and then exit via the
exhaust system as completely burned exhaust prod-
ucts.
For servicing procedures of this valve, refer to En-
gine Section of this Manual.
PART 1
SERVICE DIAGNOSIS
Condition
Possible Cause
Correction
POOR IDLING
(a) Idle air bleed carbonized or of incorrect size.
(b)
Idle discharge holes plugged or gummed.
(c) Throttle body carbonized or worn throttle shaft.
(d)
Damaged or worn idle mixture needle.
(e) Low grade fuel or incorrect float level.
(f) Loose main body to throttle body screws.
(9) Worn or corroded needle valve and
seat.
POOR
ACCELERATION
(a) Accelerator pump piston (or plunger) leather
too hard, worn, or loose on stem.
(b)
Faulty accelerator pump discharge ball.
Disassemble the carburetor. Then, use com-
pressed air to clear idle bleed after soaking
it
in a suitable solvent.
Disassemble the carburetor. Then, use com-
pressed air to clear idle discharge holes after
soaking the main and throttle bodies in a suit-
able solvent.
Disassemble the carburetor. Check the throttle
valve shaft for wear. If excessive wear is ap-
parent, replace the throttle body assembly.
Replace the worn or damaged idle needle.
Ad-
just the mixture.
Test the fuel level in the carburetor. Adjust
as
necessary to obtain the correct float level.
Tighten the main body to throttle body screws
securely to prevent air leaks and cracked hous-
ings.
Clean and inspect the needle valve and seat.
If
found to be in questionable condition, re-
place assembly. Then, test fuel pump pressure.
Refer to Specifications for correct fuel pump
pressure.
Disassemble the carburetor. Replace accelem-
tor pump assembly
if
leather is
hard,
cracked
or worn. Test follow-up spring for compression.
Disassemble the carburetor.
Use
compressed air
to clean the discharge nozzle and channels
after soaking the main body in
a
suitable sol-
vent. Test the fuel pump capacity.
Hide quick links:
Advertisement
