Pontiac FIREBIRD 1972 Service Manual page 742

6C-6 1972 PONTIAC SERVICE MANUAL
3. Follow procedures outlined in Section 6D and adjust
idle speeds to settings given in that section.
With engine running at idle, raise the adjusting screw
window and insert an Allen wrench in the socket of
NOTE: Depress or plug hot idle compensator
the adjusting screw.
valve while adjusting all engines so equipped.
With dwell meter connected, adjust dwell angle to 30
degrees for all V-8 engines. A 2-degree variation is
POSITIVE CRANKCASE VENTILATION
for wear' If a meter is
All engines have the closed positive crankcase ventilation
turn adjusting screw clockwise until engine starts to
system utilizing manifold vacuum to draw fumes and con-
misfire, then turn screw one-half turn in the opposite
taminating vapors into the chamber where
direction to complete adjustment.
they are burned. The crankcase ventilation system has an
important function and should be understood and ser-
Close access cover fully to prevent the entry of dirt
viced properly.
into the distributor.
6 CYL.
On 6 cyl. engines, 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 hose from distributor
vacuum control unit.
2. Set parking brake, start engine and run at idle speed.
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 in-
dicated, then tighten clamp bolt.
Engine Set Timing To:
6Cyl
.............................................................
CB.T.D.C.
V-8 Auto. Trans. (except 307)
....................
1O"B.T.D.C.
V-8 Manual Trans. (except 307)
..................
8"B.T.D.C.
307 V-8 Manual Trans.
................................
CB.T.D.C.
307 V-8 Auto. Trans.
....................................
8"B.T.D.C.
5. Disconnect timing light.
6. Reconnect distributor spark advance hose, then per-
form idle speed and mixture adjustment. (See Section
6D.)
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.
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 the
manifold. VALVES SHOULD NEVER BE INTER-
CHANGED BETWEEN 6 AND 8 CYLINDER EN-
GINES.
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 at 24,000 miles or
24 months, as follows:
1. Disconnect all hoses and blow them out with com-
pressed air. If any hose cannot be freed of obstruc-
tions, replace with new hose.
2. Remove crankcase ventilation valve assembly from
rubber grommet, and discard.
3. Clean crankcase and intake manifold connectors us-
ing care not to allow dirt to enter openings.
4. Replace ventilation filter in air cleaner.
5. Reinstall Crankcase Ventilation System, using a new
P.C.V. valve.
6. Adjust carburetor idle to specifications as shown in
Section 6D.
ROAD TEST
TEST PERFORMANCE OF CAR
Observe performance of engine at low speed, during accel-
eration, and at constant speed. Check for missing, stalling,
surging, poor acceleration or flat spots on acceleration. If
any irregularity is found, a complete diagnosis should be