Jeep UNIVERSAL CJ-2A - Page 24

'Jeep' UNIVERSAL and 'Jeep' DISPATCHER
c
c. To test the pump for vacuum, disconnect the
tank line and connect a vacuum gauge in its place.
Crank the engine and observe the vacuum read-
ing. If less than 8 inches [20,8 em.] of mercury
[Hg) the pump is at fault. If 10 inches [25,4 em.]
or more, check the fuel line.
C-15. Vacuum Check
Disconnect the vacuum line fitting from the head
just below the carburetor and install the proper
adapter. Connect a vacuum gauge to the adapter
and start the engine. Connect a tachometer from
the distributor primary terminal to ground and set
the engine speed at 600 rpm. Observe the vacuum
reading and interpret as follows:
a. A steady reading from 18 to 21 inches [46 a 63
em.]
of mercury [Hg.) is a normal reading indicat-
ing that valve and spark timing, valve seating,
and piston ring sealing are all satisfactory.
b. A steady but below normal reading indicates a
condition common to all cylinders· such as a leak
at the carburetor gasket, late ignition or valve
timing, or uniform piston ring and bore wear.
c. A slowly fluctuating or drifting reading indicated
that the idle mixture is incorrect and the cause
should be looked for in the fuel system.
d. A rhythmic pulsating reading is caused by a
condition affecting one or more cylinders, but not
all, and indicates leaky valve, gasket blowby, re-
stricted intake port, or an electrical miss.
e. An intermittent pulsating reading is caused by
an occasional malfunction such as a sticking valve
(all valves may be erratic in operation if the valve
springs are weak), and electrical miss caused by
insufficient distributor point tension or low coil
voltage coupled with inconsistent spark plug gaps
or fouled plugs, or dirt in the fuel system fi.nding
its way into passages of critical size or valve seats
in the carburetor.
f. A normal reading that quickly falls off (with
engine running at 2000 rpm.) indicates exhaust
back pressure caused by a restriction in the exhaust
system.
g. Make indicated corrections or advise vehicle
owner of engine condition.
C-16. Adjust Carburetor
Refer to Fig. 29 ·
Before adjusting the idle speed and mixture, start
the engine and allow it to run until operating
temperature is reached. Then proceed as follows:
a. Set the idle speed adjusting screw. Do not set
the engine idle below 600 rpm.
FIG. 29~-CARBURETOR
1-Idle Speed Adjusting Screw
2-ldle Mixture Adjusting Screw
b. Adjust the idle mixture adjusting screw to
provide smooth idle. For richer mixture, turn the
screw out; for leaner mixture, turn the screw m.
Normal opening is% to 1% turns.
C-17. Check Fan Belt
Inspect fan belt for serviceability and proper
tension. Correct tension is obtained when thumb
pressure midway between pulleys causes the belt
to flex Y2" [1 >-4 em.].
C-18. Road Test Vehicle
After completing the tune-up, road test the vehich
for power and over all performance. Make necessar~
adjustments.
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