Pontiac tempest 1968 Service Manual page 344

E N G I N E T U N E - U P
6C-5
adjustment on the vehicle. Whenever possible, a
dwell meter should be used for better accuracy.
V-8
1. With engine running at Idle, raise the adjusting
screw window and insert an Allen wrench in the
socket of the adjusting screw.
2. With dwell meter connected, adjust dwell angle
to 30 degrees for all V-8 engines. A 2-degree varia­
tion is allowable for wear. If a dwell meter is not
available, turn adjusting screw clockwise until en­
gine starts to misfire, then turn screw one-half turn
in the opposite direction to complete adjustment.
3. Close access cover fully to prevent the entry of
dirt into the distributor.
6
C Y L
On 6 cyl., adjust point gap with a flat feeler gauge
to .019" (new) or .016" (used).
TEST IGNITION TIMING AND ADVANCE
1. Attach a timing light and tachometer as shown
in Fig. 6C-1.
NOTE: Disconnect both hoses from dual acting
vacuum control unit.
2. Set parking brake, start engine and run at slow
idle speed (solenoid inactive).
3. Aim timing light at marks on lower timing
chain cover and harmonic balancer.
4. Adjust timing as required by loosening clamp
bolt and rotating distributor until correct timing is
indicated, then tighten clamp bolt.
5. Disconnect timing light.
6. Reconnect distributor spark advance and retard
hoses, then perform idle speed and mixture adjust­
ment. (See Section 6D)
6 Cyl. 4 Bbl. 5°BTDC
6 Cyl. 1 Bbl. 0°TDC
V-8 (All) 9°BTDC
IDLE SPEED AND MIXTURE
1. Connect tachometer to engine. Set parking
brake. Start engine, allow to idle.
2. With a thoroughly warmed-up engine, check to
see that choke is fully open and carburetor is on slow
idle.
3. Adjust idle speed and mixture screws to give
proper idle speed.
NOTE: Depress or plug hot idle compensator
valve while adjusting all engines so equipped (6
cyl. 1 bbl. with A/C and 6 cyl. 4 bbl. only.)
Follow procedures outlined in EXHAUST EMIS­
SIONS SECTION and adjust idle speeds to settings
given at end of that section.
POSITIVE CRANKCASE VENTILATION
All 1968 engines have the closed positive ventila­
tion systems utilizing manifold vacuum to draw
fumes and contaminating vapors into the combustion
chamber where they are burned. The crankcase
ventilation system has an important function and
should be understood and serviced properly.
In the closed crankcase ventilation system, air is
drawn through the engine, through a regulating valve
and into the manifold, drawing crankcase vapors and
fumes with it to be burned. The closed positive
ventilation system draws the clean air from the
carburetor air cleaner and has a nonvented oil filler
cap.
The P.C.V. valves are designed specifically for
each engine to control the amount of flow from the
crankcase to manifold. VALVES SHOULD NEVER B E
INTERCHANGED B E T W E E N 6 AND 8 CYLINDER
ENGINES.
The crankcase ventilation valve should be checked
at regular intervals otherwise it will become plugged
and ineffective.
The P.C.V. system should be serviced as follows:
1. Disconnect all hoses and blow them out with
compressed air. If any hose cannot be freed of
obstructions, replace with new hose.
2. Remove crankcase ventilation valve assembly
from rubber grommet, and discard.
3. Clean crankcase and intake manifold connec­
tors; using care not to allow dirt to enter openings.
4. Clean and re-oil ventilation filter in air cleaner.
5. Reinstall Crankcase Ventilation System, using a
new P.C.V. valve.
6. Adjust carburetor idle to specifications, sec­
tion 6D.
R O A D T E S T
TEST PERFORMANCE OF CAR
Observe performance of engine at low speed, dur­
ing acceleration, and at constant speed. Check for