Chevrolet 10 Series 1970 Service Manual page 330

ENGINE 6-8
F ig . 14—S e ttin g P oint D w e ll
V8 ENGINES
• With engine running at idle, ra is e the adjustment
s crew window and in sert an A llen wrench in the
socket o f the adjusting screw (fig. 14).
• Turn the adjusting screw as requ ired until a dwell
reading o f 30° is obtained. A 2° variation is a llo w ­
able fo r w ear.
• C lose acce ss c o v er fully to preven t the entry of
d irt into the distribu tor.
NOTE:
If a dw ell m eter is not available, turn
adjusting screw clockw ise until engine starts to
m is fire , then turn screw on e-h alf turn in the
opposite d irection to com plete adjustment.
IN LIN E ENGINES
• Rem ove d istribu tor cap and rech eck point setting.
If dwell is s till not within sp ecification s check the
distributor as outlined in Section 6Y.
Check Dwell Variation
Slowly a cce lera te engine to 1500 rpm and note dwell
reading. Return engine to idle and note dw ell reading.
If dw ell variation exceeds sp ecification s, check fo r worn
F ig . 15— Ig n itio n Tuning M arks
W IN D O W
"H E X " TYPE
ADJUSTING
SCREW
distribu tor shaft, worn distributor shaft bushing o r loose
b rea k er plate.
Check and Adjust Ignition Timing (Fig. 15)
1. Disconnect the distributor spark advance hose and
plug the vacuum source opening.
2. Start engine and run at idle speed (See tune up chart
in Specification section.
3. A im tim ing light at tim ing tab.
NOTE:
The m arkings on the tabs a re
increm ents (the grea test number of m arkings on
the " A " side o f the
is TD C and a ll BTDC settings fa ll on the " A "
" O" .
(advance) side o f
4. Adjust the tim ing by loosening the distribu tor clamp
and rotating the distributor body as requ ired, then
tighten the clam p and recheck.tim ing.
5. Stop engine and rem ove tim ing light and reconnect
the spark advance hose.
Adjust Idle Speed and Mixture
NOTE:
On veh icles equipped with E vaporative
E m ission (R PO NA9) disconnect " F U E L T A N K ' '
line from vapor canister.
E vaporative Em ission System .) A fte r tuning en­
gine, reconnect " F U E L
can ister.
1. With engine running at operating tem perature (choke
va lve and, if applicable, a ir clea n er damper door
fully open) a ir conditioning off, and parking brake on -
adjust idle speed and m ixture as follow s (See "T u n e -
U p " D ecal F ig. 16):
L6 ENGINES
• 10 S eries
Disconnect and plug distribu tor vacuum line.
Turn m ixture screw in until ligh tly contacting seat,
then back screw out four turns.
Adjust solenoid screw
manual transm ission
automatic transm ission in d rive (fig . 17).
Adjust m ixture screw
manual transm ission
F ig . 16—T u n e -U p D ecal
in 2°
" O" ). The " O " marking
(See Section 8 fo r
T A N K " line to vapor
to obtain 800 rpm with
in neutral; 630 rpm with
in to obtain 750 rpm with
in neutral; 600 rpm with
CHEVROLET TRUCK SERVICE MANUAL